Try removing the One SLs as surrounds in the Sonos app and swapping the speakers. Then add them as surrounds again.

Ill give that a try this evening, I’ll report back. 

I can confirm that did not resolve the issue. 

SonosNet isn’t exactly a standard WiFi signal, which is why standard WiFi devices don’t show it, but it uses the same channels so other WiFi devices can impact it. It is also subject to other 2.4 GHz and 5 GHz interference.

Since you have the Arc wired you should be able to look at the Network Matrix and see if it is showing any issues.  Use the Arc’s IP here: http://0.0.0.0:1400/support/review

The surrounds should be connecting on a 5 GHz channel and automatically picking a clear one. You don’t by chance have them connected to Ethernet too?

Do you have other WiFi or RF emitting devices close to the Arc or surrounds, within about a meter? If so can you do a temporary move to get that much clearance?

A major pain, but one I had to use to find my problem here, is to power down your other gear and see if Sonos starts working. If it does plug about half the gear back in and test again. Keep it up until you find the problem device. In my case it was an external hard drive, not even a radio in it, just horribly RF noisy electronics.

Thanks for your input, I’ll try that out tomorrow. Unfortunately only the arc is connected via Ethernet. The TV is wall mounted with the arc directly below it, also wall mounted. I don’t have many things nearby that may be causing interference. 
 

I do have a 5 GHz wifi, but that router is quite far away (maybe 45 feet away) I can try locking the 5 GHz wifi to a specific channel? 
 

The closest device to the ARC is the cable box (I’m with Vidéotron in Quebec, which is some type of iptv box really) but I tried disconnecting it from the TV and turning it off and it didn’t resolve the issue. 
 

My oven which is maybe 30 feet away emits a wifi signal. Ill also try disconnecting electronic devices that are nearby although nothing is within 1m of the arc really. No new electronics nearby since June either. 
 

I’ll have a look at the network matrix to see if anything seems odd when I get the chance tomorrow and report back! 
 

I currently have the home 2.4 ghz wifi on channel 1 with Sonos set to channel 6 and it hasn’t resolved anything. 

@ajad26, 
What happens if you uncable the Arc from the LAN and run it (all Sonos devices) on your WiFi signal instead?

Hi @ajad26 

Welcome to the Sonos Community!

Given that there’s no sign of interference or transmission issues on your system, something is not working like it should. To narrow down the issue I recommend removing the surrounds from the Arc, physically swapping them over, then bonding them back to the Arc again.

Remove surround speakers

Add surround speakers to a Sonos home theater

As you have already tried factory-resetting your whole system, whatever the result is of the test above, I recommend you get back in touch with our technical support team. If the issue followed the speaker to the left, then that One SL likely has a fault and needs replaced. If the issue sticks to the right, then the Arc is likely the device with an issue, or there’s something about the location of the right speaker.

I have a feeling this won’t be resolved without something being replaced - it could be the location of the right speaker (interference, or maybe it’s just in the corner of two thick walls), but I don’t see evidence of this in the diagnostics.

I hope this helps.

Edit: I’ve just been advised the RR One SL seems to have a fault. I’ve added notes to your existing case.

Awesome, I’ll give the tech support a call later this afternoon when I get back home. I was listening closely yesterday and the issue does indeed seem like its coming from one surround only. 

Appreciate the input, will update the thread afterwards! 

FYI Sonos will be sending me a One SL under warranty as it appears the RR One SL is indeed faulty. 

Hi @ajad26 

Fantastic! Thanks for updating the thread! 

Please remember to remove the surrounds from your Arc before sending the speaker away to pave the way for the replacement being added.

Hey so I haven’t received my new One SL, but I was doing further testing and I am now 100% sure that both One SL surrounds are out of sync with the arc. (Did this by scrolling on the TV menu and listening for the “ding” while scrolling). 
 

Is it possible to check if both surrounds are affected by the same fault or could it be the arc that is faulty? 
 

I just ran a new diagnostic after I did the ding test: 1812713748

Hi @ajad26 

My sincerest apologies - the LR speaker does indeed show the same issues as the RR, but the out-of-sync issue was not, in this case, reported in the diagnostic’s summary so I didn’t really investigate that speaker enough. Also, it's very rare for two speakers to exhibit the same fault on one system.

Again, I have added notes to your existing case - please get back in touch to arrange a second replacement.

I did of course then take a closer look at your Arc - other than a lot of 5Gz channel hopping, it looks okay. The channel hopping may well be an artefact of the faults the surrounds have, so we’ll wait and see how things go once both surrounds have been replaced.

Perfect, I will be in touch with them once they open. 

Would it be worth trying to lock the routers 5 GHz wifi network to a specific channel in the meantime to see if it resolves the issue? 

Hi @ajad26 

If the router is at all close to the Arc (it certainly doesn’t look like it), you would probably have more success just separating the two. In theory, however, yes - it’s just a question as to whether your router allows you to do so. If it does, I recommend it (after checking which channels are clear in your locale).

If there aren’t any devices near the Arc transmitting 5GHz, then I’d put the behaviour down to the SLs’ issues.

Gotcha, the router is indeed about 45 feet away from the Arc, so it is unlikely. I’ll check for the clear channels and see if it helps although it does seem that the issue is the SLs. The sub which is not connected to an ethernet cable has never appeared out of sync, allowing me to believe that the issue is strictly related to the surrounds. 

Hate to be the bearer of bad news but the issue persists with the replacement One SLs. 

latest diagnostic: 951989083

At a loss as to what it might be now. I will try all the usual trouble shooting shooting steps in the meantime. 

Hi @ajad26 

Apologies for the delay - I’ve been on holiday.

Some time after my last reply to you, I was informed by a colleague that it may indeed be the Arc that was at fault, but that we still needed to verify the fact by replacing that last surround speaker.

I can only apologise for the time (and effort) this is taking to resolve, but with the replacement of the Arc, there won’t be much left to go wrong again. Please get in touch with our technical support team one more time and report that you’re still experiencing these sync issues.

Note that there is a possibility that the Arris router is at fault, so please test with the Arc connected to ethernet if you haven’t done so since replacing the second surround speaker. Thanks.

I hope this helps.

Hey! 
 

Thanks again for the reply. The arc is indeed connected via Ethernet and the sync issue has been persistent. 
 

I’ll give the technical support a call to see what they can do about the arc. Have you put a note in the file already? 

Hi @ajad26 

Yes, but some further troubleshooting may be required. Procedures have changed since I was in technical support, and Europe (where I am) and America had differing procedures to start with.

Perfect thanks Corry, I’ll give them a call from home after work, will report back!

Replacement arc has been sent out, hopefully this will be the solution, fingers crossed! 
 

I’ll update the thread after I receive it. 

So I’ve had my replacement arc for 5 days now and so far, the audio issues have been fully resolved! Seems the faulty Arc was the culprit all along. 
 

Thanks again Corry for all your help and to all those who have contributed. I love my Sonos setup once again!

Hi @ajad26 

Fantastic news - thanks for updating the thread!

I’m sorry it took what it took, but glad that it’s been resolved in the end.

You are most welcome!