First thing I’d do is look at the steps to submit a diagnostic to Sonos support so the next time it happens you will be able to do one fairly quickly. The logs seem to cover about 15 minutes but I’d try to be on the early side of that. You might also want to submit two or three diagnostics as some seem to arrive at Sonos corrupted.

Once sent contact Sonos support with the number(s) and describe the problem to them. You could also post them here and they will usually be seen, Sonos staff here is a bit thin and has limited capabilities compared to the phone crew.

Now that I know to do that I can definitely do it within 15 mins.

It finally happened again and I submitted diagnostics

What was the resolution? Sounds like it’s still happening to some Arc owners

I haven’t heard it in a really long time but I also haven’t played music off the arc very much because of this issue (which is a huge bummer after spending this money).  The resolution was they wanted a recording of it and while at first I was willing to setup the infrastructure to get a recording of this, slice it and send it to them, I really didn’t think it was necessary for them to believe me or DX the problem. I gave them timestamps and logs TWICE, that’s more than enough to start looking.

Nothing was ever done but I also never heard it again after the initial 6 times or so.  I’ve read the description of the popping sound in arcs that continues and it DOES NOT seem like the same issue as mine.  Mine isn’t so much a popping sound as a much as it is a loud random tone that plays and only happens when the arc is involved.

Inconclusive is the best I can tell you, sorry.

There are similar new reports on the Sonos facebook group. Looks like it’s still happening to people

This happens to me, too. I restarted the Sonos, appletv, and my Vizio tv. Now it just happened again for the second time this week after months of nothing. 

Whenever you want to get it fixed submit the diagnostic, call Sonos and let them solve the problem.

This is a community, user to user forum so none of us can see the diagnostics and the forum admins (Sonos staff) may see your post and try helping but they don’t have all the tools the Support staff have available.

It happened to me again the other day. Seems like it hasn’t happened in months but honestly it’s so jarring that it negatively impacted my listening behavior in this room. 
  When it happened earlier this week it was just awful.  The hair was standing on the back of my neck for 30 mins after. 

Same problem, frightens me and our dog to death. Sending diag to Sonos now!

Just got chat terminated half way through having waited 30 mins for agent. Now waiting for call back after being told 80 minutes wait on phone. 

I have eliminated the possibility that it was microwave interference. One of the times it happened it happened while the microwave was running and another time exactly when I opened it but it happened again in the last two weeks and the microwave wasn’t running. 

Happen to me as well. Yesterday evening around 8 and this morning just after 6am.

It sort of sounds like the Netflix when it starts. Because it’s so loud and frightens you.

This just happened to us this morning. One of our stereo-paired Roams went offline (as usual) and this time I grouped to our Arc setup, then ungrouped the Roam setup and regrouped it. That fixed the speaker drop out. A few minutes later we thought our home had been destroyed by an electrical failure, alien pulse beam or something. OP described the sound accurately. Yes it was bone chilling. I ran into the living room expecting a fire. Both our hearts remained pounding for some time. Then it happened again about an hour or two later. I’ll leave it on today and try to get audio recordings. 

 Sergeantpup2 - I know it’s been a while since you posted this but I have a similar system throughout my home and just recently I experienced the EXACT bone chilling noise! Did you ever find out what caused it?

No, there was a few posts ago where somebody had it happen multiple times in a short period and they were going to try to get a recording because that’s the last thing SONOS asked for before they would even touch this issue. It’s still happening. It happened to me within the last month. 

Just happened to me for the second time. Same as everyone described. Very alien and startling sound. Stops after a few seconds and everything resumes as if it never happened. 

I would perhaps just follow @Stanley_4’s advice in his answer to this thread.

Don't bother unless you have a recording. Several of us have sent diagnostics and all SONOS says in return is that we need a recording of a 5 second sound that can happen any time over a period of months. 

Does it not occur frequently then and can it not be easily reproduced? I have the Arc in the Living Room (used all day/most days), but can’t say I’ve ever encountered the issue.

it just happens randomly.  Sometimes I don’t hear it for weeks or months and sometimes that’s just because I don’t listen to it as much because of the problem.  It’s definitely not reproducible on demand.

So it’s quite a difficult issue then, particularly if it’s an ‘event’ that maybe does not show up in a Sonos diagnostic report. Not sure how to go about capturing the data to give to Sonos for such an issue. I bet Sonos engineers will have difficulty reproducing the problem too.

I just returned my Arc last week and they are replacing with a new arc. Exact same shrieking as you all described? I’m curious, anyone who received a replacement had it happen again…? 

Just another possibility.…

Most probably have never owned a radio outside of what is installed inside your automobile (motor car for my UK friends ).

Radios in my day were either tube  powered by electrical current and eventually electrical or battery powered with a component called a transistor that replaced the tube compnent which coined the descriptive  phrase "transistor radio". If they were still produced today the transitors would be replaced by what most of you know as an "integrated circut board".  

Transitor radios were subject to interference and sometimes produced weird noises especially around overhead powerlines. I can remember briefly hearing a telephone conversation through my transistor radio.

OK enough of the history lesson...however, the Arc works over WiFi and/or Ethernet. The latter is much less prone to interference as WiFi might be . However, Ethernet can be subject to interference when the shielding is inadequate especially if in close proximity to other wires such as power cables from a TV, AV system, Appliances, computers....the list of possibilites is infinite. Point being that WiFi is even more vulnerable. 

I've only mentioned the above as a possibility; as the occurences appear to be very random and un-reproduceable. That said if anyone receives a replacement Arc and the weird noises continue then I'd look to environmental influences that may be causing the issue. 

I get the same or similar loud random noise coming from my Arc while watching TV. 

My best guess would be a notification coming through from sonos altho I've never checked.