@PG80,

I see from your earlier posts, you initially had a Yamaha HT setup and switched to the Sonos Arc, surrounds & Sub, but then had some difficulties with earlier Sonos updates, leading you to post on a few occasions in the 14.12 thread, stating that your setup sounded muddier. 

I assume after that then, you switched away to the Sony HT setup, but found you still preferred the sound of the Arc HT over the Sony system and have now decided to switch back.

Is it the case you have put the setup back in the same room/position, where it was before, or is it now in a different room/location?  

If it’s the latter, have you perhaps left the HT setup tuned to its previous room (assuming you just powered off the setup and set the speakers aside when you swapped things out for the Sony system)?

If so, then in the first instance, I would simply try Trueplay tuning the HT setup again, as that can sometimes help to sort the issue… if tried already, then perhaps give it another go with a different iOS device, if you have one to hand, or can maybe borrow one?

I’m no electrician, but I would not have thought the EU/UK power adapters would be a part of the cause of the issue mentioned, but I guess you can always go back to powering the devices as you did previously, just to see if that does make a difference, but (I agree) using the approved adapters sound like the much safer option to me.

The Yamaha setup is unrelated. It was in a different house, different TV, sometime ago.

The Sonos is now placed exactly where it was before. And I'm using with the Trueplay tuning I had before the system switch. So i don't understand why I have these issues.

Could the other system have messed with the TV? But eARC is set to Auto and audio is set to passthrough so I'm not sure that's it.

Maybe within 20 minutes of hearing the issue, submit a Sonos diagnostic report from the ‘Settings/Support’ area of the Sonos App. Make a note of the reference generated, and when practicable, contact/chat to Sonos Support Staff about the matter via this LINK and see what they can suggest. They maybe able to see if there is any issues with the incoming audio from the TV.

Ok i will do that. Is there a way to know if any of the speaker drivers are damaged?

Apart from looking at the teardown of the Arc to first see where each speaker is located and listening to either the output balance overall, or better still, listening up close perhaps using a cardboard tube etc; the diagnostic report will likely reveal if there is a hardware fault for you, but check that with the Staff when you speak with them. The speaker might have got damaged in the move around perhaps, or it might be the TV, cabling, or just a tuning issue. Too early to say, so perhaps start with the diagnostic report and speaking to Sonos Support.