You’ll need to take this up with SONOS phone support. How old is the unit? Don’t disassemble the unit and attempt DIY repair before contacting support. Units that have been disassembled will not be accepted for exchange or credit.

Thanks, I went through diagnostics with the team and no fix unfortunately. Unit out of warranty alas. Seems to be an issue with the inner workings. Will soldier on with current set up for time being as can't afford to replace even with 30% off voucher to send it back.

Hi ​@joshimoto 

Welcome back to the Sonos Community!

Sorry to hear about your Amp buzzing from the unit - I myself got an Amp from the office that did exactly this. I am glad to report that after consulting an engineer (perk of the job, I guess), who said that it was likely just a component in the PSU and therefore would be contained if it failed, I kept it on and after a day (I think - certainly not much longer) of getting quieter, it stopped buzzing. I left it on and kept using it for several years.

I just plugged it back in for the first time in a while (it got replaced by an Arc Ultra) and it buzzed softly, but it is a nice day today, and it was probably cold when I got it. So, I’m going say that if it sounds like mine did, it’ll be fine once it warms up a bit. What did mine sound like? Well, I looked up the conversation in my chat history and I described it as “high-pitched but modulated by 50Hz” at the time. So, a mains buzz more than a mains hum, if you will, which sounds like what you are describing.

However, my Amp had been on permanently for couple of years at least, then off for about 1 year, before I got it - if your Amp has been in constant use and started making this noise, I doubt it will go away.

If you smell any burning from the Amp, please immediately unplug it from power and don’t touch it for a while, then discard for recycling. If the buzz itself is not completely regular, please unplug it from power, and recycle.

If you decide to use it, please do not try to muffle the sound (unless using a cabinet) - instead, see if you can reroute the speaker wires to a spare room, for example, so the noise does not bother anyone.

I hope this helps.

Thanks so much for the detailed and contextual reply it is much appreciated. The Amp was been stored for about a year before setting up again so will try leaving plugged in and monitoring over a period of days. Interestingly the buzz seems to modulate with the status LED on the unit - not sure if there is a connection but interesting nonetheless. Thanks again.

Just following up after a week or so since the issue raised its head. Following Corry P's suggestion I have left the Amp plugged in and after 3 days or so the electrical  buzz disappeared and hasn't returned (so far, touch wood).

Big thank you to Corry P for the suggestion and an interesting one for Sonos support to note as (granted support is difficult to provide from a remote location) there can sometimes be simple solutions to issues that don't require a faulty return/trade up. Very happy with the outcome so far and testament to the value of fora like these. Thanks everyone. 

Hi ​@joshimoto 

Thanks for the update, and I am glad to hear it!

I’m surprised that a modern unit would exhibit this characteristic. This was a somewhat common (especially tube amplifiers) trait in much older units. The capacitors in the power supply would “deform” (a type of degradation associated with non use), resulting in hum. After the capacitors are used for a while, they begin to reform. In the deformed state the value of capacitance decreases. The value is associated the ability to reduce hum.

In very old tube units left unpowered for a few years, the power supply capacitors often failed catastrophically at power up. The trick to avoid this failure was to slowly ramp up the power line voltage over a period of days. This allowed the capacitors to reform safely. Power supply design for solid state units has dramatically changed from those old days and the ramp up trick is not likely to be effective on modern units.