If you’ve power cycled it, I’d call Sonos Support directly to discuss it.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Hi,

Did you get anywhere with this?

I have the exact same experience, unpacked after moving (stored in it's original box for about 4 months) and I'm getting a squeel I've never heard before!

Since moving I've bought a gen3 sub to pair with the playbar but the squeel is driving me mad!!

Thanks 

It is possible that this is a mechanical noise originating from the power supply, not the speakers. This mechanical noise is typically louder in the lower left rear when you are facing PLAYBAR’s front. Regardless of cause, it’s annoying. The power supply noise is usually independent of music and Volume setting.