Extremely disappointing answer for all the people that has been extensively troubleshooting and reproducing the issue and giving mountains of data and details in this thread... 

I purchased the Beam Gen 2 yesterday as my first Sonos product, specifically to use with PS5 and LG C1 48. This is absolutely a specific issue related to the Beam and not LG.

I have used numerous other audio equipment, in a multitude of formats both with PC and PS5. No such issues with any other products. The audio drop outs with LPCM 5.1 are extremely disappointing. It is not acceptable to suggest the purchasing of a non-CRC Hdmi cable, or to switch to a compressed audio format (e.g. Dolby) as workarounds. Further to this, passing the buck to another manufacturer (LG) is not acceptable when there are no reasonable or methodical grounds to suggest doing so. I do hope that this fault is resolved soon, or the Beam will be returned and shall be my last Sonos purchase. 

Don’t hold your breath for a fix. This has been going on for a year now. If this bothers you, return it.

Ok, thanks for the reply mate. In fairness, as others have also done I have just tried dolby 5.1, during which the issue no longer occurs. Compressed/lossy audio isn't ideal for a fairly expensive device but it's still a considerable audio improvement over TV speakers. 

For PS5 you can set it to 7.1 it’s the same as 5.1 and has no problem.

But this won’t work for example with Nintendo switch which only does 5.1 LPCM.

Interesting, could you explain how the LPCM 7.1 is the same as 5.1 if you know why, please? If I were to guess, I would assume that either the 7.1 can be down mixed to 5.1 by the Beam, or the extra two channels are effectively "empty" placeholders within the audio formatting? 

As far as I understood from people who researched it, they’re just empty channels. The Sonos app will show you 7.1 when you select soundbar as source type, but it’s actually 5.1.

As I'd suspected, then. Thank you! 

As indicated in OP’s first post this isn’t true.

Checking OP’s timeline:

1. ​​​​​​​They were able to use their Beam on PCM 5.1 flawlessly
2. They installed the Sonos 14.10 update which upon googling is a MAJOR update
3. They started encountering PCM 5.1 dropouts
4.  They installed the LG firmware update AFTER they were already having dropouts

So it’s complete and utter hogwash to place the blame on the LG firmware update. On the contrary, it was after applying the MAJOR Sonos 14.10 update that messed things up.

Have been following this thread for a while after recently purchasing a beam, and 2 era 100s. Tv is LG C3 Oled 55”. I was originally just going to confirm that the problem persisted on C3 with the PS5 as someone a few pages back had asked about the C3 model. Regular streaming from the TV itself is fine. (whether it’s 5.1 or dolby atmos) My switch wasn’t working with 5.1 until I plugged it into hdmi slot 1.

However, after a TV firmware update yesterday I can confirm that the PS5 isn’t dropping out anymore when set to 5.1. I tested this by playing about 30 minutes of hogwarts legacy, and confirming on the sonos app what the output was. Software version for the TV is 03.11.10. Not sure what changed or what was updated. Also worth mentioning that I had unplugged the PS5 hdmi for a few days, though not sure that had any effect. 

Anyway just wanted to share that news, in case anyone else with similar tv models can update and test. Hope that helps! 

I've just updated my C1 from 03.34.80 to 03.34.95 with  no change, dropouts still every 59 seconds. At least that means I can still reproduce the issue to try a couple of ideas out. 

@Retcon It’s widely documented that this issue can come and go at random. I suggest you test as much as you can if ever you’re planning to return your Beam. Would be nice though if it really got fixed for you as all we got from Sonos is “LG will fix it. Source: trust me bro”

Maybe it would be a good start for Sonos to do a complete test before shifting the blame to LG. Maybe using the extensive testing the community on this thread have done as a starting point. 
 

You would think Sonos would care a little more if one of their products isn’t super compatible with arguably the most popular high end tvs? 
 

There is a reason why this thread is growing and growing, maybe people with good sound equipment also have arguably the best OLED tvs? Shock 

While the issue is not resolved what are the best settings for the Beam Gen 2 and PS5? 7.1 LPCM or 5.1 Dolby/DTS?

I observed two new things today:

1. I had the opportunity to swap out the Beam2 out for an Arc in my setup and compared the 11111 diagnostics for "Sonos test card" on HDMI2 over an unmofidied cable. There is a difference in the reported audio formats (albeit that both have silent audio):

    Arc: PCM 2ch 0Hz | N:0, CTS:0, LayoutValue:0, Channel Status: 2
    Beam2: UNKNOWN 9Ch 88200Hz | N: 6262, CTS: 42092, Layout Value: 0, Channel Satatus: 9

2. I finally got round to splicing a Rapsberry Pi TMDS video signal with the Beam 2 control/eARC signals. Pins 1-12 connect the RPi to the TV which replaces the Beam2 test image with the RPi console. Pins 13 to 19 connect the Beam2 to the TV's CEC, DDC and eARC. On power up, the TV was using CEC to operate the Beam2 volume, which was a good start, but needed tweaking to get the setup operating like for like:

• toggled "eARC Support" off/on in the LG TV as it had fallen back to ARC mode (LPCM 2.0) despite indicating that eARC was enabled. Once eARC was re-negotiated LPCM 5.1 played from the HDMI3 source.
• used tvservice command to force enable the RPi HDMI output - since it has no DDC wires connected and therefore no EDID, the RPi doesn’t know what resolution to use so disables HDMI. Mode 34 sets 1080p@30Hz (same as the Beam2 test image):

sudo tvservice -e="CEA 34 HDMI"

At this point, choosing HDMI2 on the TV showed the RPi video signal. Then, switching the TV input to HDMI3 plays LPCM5.1 out of the Beam2 with no dropouts. I can change HDMI2 video modes in the "background" with tvservice (e.g. 720p or 24Hz) without interfering with the eARC audio stream. However, given the observation in #1 I thought I'd try to get the RPi to output 8ch audio into HDMI2, as currently the audio stream is disabled entirely (as per ARC).

I changed input back to HDMI2 and used speaker-test (as I had previously to force 8ch sound). I was surprised to hear it play out of the Beam2, but I guess this should be expected - the TV is just routing the audio received from the selected HDMI input into its eARC circuit and back out to the soundbar, just so happens that it's the same HDMI port for both in this case. I switched back to HDMI3 and Beam2 played LPCM 5.1 without dropouts.

sudo speaker-test -c8

Then I thought I'd change the HDMI2 audio from 48Khz to 88.2Khz (to match the Beam2 diagnostics) and a dropout occurred immediately, but did not repeat. I quit speaker-test and restarted, another drop out. I repeated this and checked on HDMI3 11111 and could see the audio format blip occasionally, in the same way as when the Beam2 drops out.

With the sacrificial cable in this new configuration I can also patch the Beam2 video signal back in to the TV. There's a drop out as soon as the connection is made, then repeating every 59 seconds.

I repeated the tests with the same source on HDMI1: no dropouts (as previously discussed), even when trying to force them with speaker-test.

I repeated the tests with the Arc, no repeated dropouts but I could force them with speaker-test when the LPCM5.1 source is HDMI3 and the video spliced to the RPi (and could not when the source was HDMI1).

I'm thinking that #1 and #2 mean Beam2 is doing something unusual to the audio signal in its "test card" output (into HDMI2) which the LG TV is sensitive to on HDMI3. I can't tell what the odd behaviour is, whether it's close to tolerance, undefined, invalid or just dropping/handshaking. Whatever it is, LG TV is sensitive to it on HDMI3 but not HDMI1 (anymore).
 

@RANDUSR23296 has done more than Sonos ever did (w/c is actually nothing). Sad that they can’t even be bothered to lift a finger despite all the evidence shared here by the users.

 To recap, Sonos’ response to this situation after ~1 year and ~400 posts:

1. No technical investigation that cleared the Beam of any fault
2. Place the blame on LG because numerous unrelated results come out when you google for “LG OLED 5.1 issue”
3. Claim that LG will fix it with source being “trust me bro”
4. Refuse to elaborate further. Leave

@ste_ms tagged the mod on a post from a week ago and they have not yet responded. Considering that monitoring this place is literally their job, unless they are on holiday, it is clear that Sonos had already  ducked and ran.

To potential buyers or those within the return period: if you’ve come across this thread, take heed and stay away from Sonos.

I think an internal investigation could have happened (rather than just auto-timing out their Jira ticket after 12 months). It's easy enough to reproduce, should be easy to spot in a lab with industry test gear, but Sonos may now have chosen not to publicise the results based on their discoveries.

If it turned out that only a hardware modification could restore stability then I can imagine any company involved  being much more cautious about admitting a fault/offering a fix, maybe hoping that another stake holder would back down first. The RMA costs would be considerable, so too would the reputational impact of shipping a hardware fault. 

It's rather ambiguous from Sonos’ response whether they have actually been talking to LG or not before deciding to walk away. There does seem to be evidence of LG trying to mitigate the problem, by at least stabilising HDMI1, but again they could be limited by hardware at this point. I only search for English language forums, there could be LG discussions going on outside my language bubble. Sonos are tiny (by market cap.) compared to LG so may just have the same communication issue with LG that their consumers do. LG have the upper hand here as there's still no evidence offered on this thread of any other eARC device than Beam2 triggering the TV to drop PCM5.1 over eARC.

Seems to me a change from either company would resolve the issue sufficiently. It's a poor response from Sonos whatever the situation:

- they know the cause and won't fix

- they don't know yet so can't fix

- don't want to know and have done nothing for 12 months.

Edit: to be fair, it is also possible that Sonos have investigated and their conclusions are covered by some kind of NDA...

Just to give an update, the dropouts came back, not sure if there was another Tv or sonos update since my last post. I’m just using ps5 with 7.1 and seems pretty good so far with miles morales. Was curious if there was any xbox users here as I have’nt seen any mention for settings working with series x. Need to hook mine up and see what the options are. 

Also curious as an experiment, since hdmi slot 1 seems to work (have been playing zelda totk without issue this way) if using an HDMI switcher might help? Most of the switchers are 4k and 60hz, which would potentially cap framerate depending on the console/display. 

Why buy a switch when you can buy a one way optical HDMI cable to fix it? See my posts a few pages back about this workaround if you haven’t seen it. 

I guess a switch would be operating all signals as intented, whereas blocking the Beam2 video by whatever means could be interpreted as out of spec for Warranty purposes.

Maybe this sort of thing would be sufficient:

https://amzn.eu/d/feSCeXi

My experiences with switches involving  HDMI though are that they either miss some vital capability or are annoyingly slow.

5.1 PCM started to work fine with PS5 and LG CX 3 days ago. It worked perfectly for two days, 3-4 hours of gameplay each day and no cutouts at all, until I had to cut power from all three devices, and now the issue is back again. I wonder what did I do to make it work for 2 days?

EDIT: I just read this thread a bit more and realized that the same happened to a lot of people before, but then the issue came back again. Sigh...

Thanks for taking the time to post the new data point. It seems that LG C3 chipset isn't drastically different to C1/C2.

Indeed, power cycling the Beam2 should re-instate the dropouts immediately.

Sorry, maybe I was unclear. I have an LG CX, not a C3. 

Ah, got it. Sorry, I misread your post. It was @Retcon with the C3, I should have scrolled up to double check before replying.

Anybody seeing a change on 15.5?