While we cannot rule out hardware failure, this seems like a smack the forehead type of issue. What is CONNECT operating into? What is CONNECT’s input? Is CONNECT’s Source Level setting correct? 

What Amplifier/Speakers is the ‘Connect’ currently linked to? You mentioned different speakers, but assuming they’re not all ‘active’, have you tried another Amp/Receiver etc? 

For years the Connect received input from a Numark mixer; currently I am simply trying to play Spotify from its own integrated player. The output transfers to a basic Panasonic hifi, with which it never had any troubles for years now (and I tried different setuos to make sure that it is not the hifi aux which is broken). Where can I set the source level? :)

If you’re playing Spotify from the Sonos App out to your HiFi, the line ‘source level’ is irrelevant and was why @buzz was asking about the source input. Have you got another Amp that you can try, a headphone Amp perhaps, or a Bluetooth transmitter etc?

Also, have you tried switching the Connect between fixed and variable audio output? Check too that the HiFi has the correct aux input selected and that it’s own volume control level is not set low.

Connect is set on variable, hence I hear the silent sound when setting it to max. Hifi is otherwise working fine, also with its aux. I tried previously other amped speaker and now the bluetooth transmission with a headphone as well - same result.. :(

How about if you switch the ‘Connects’ audio-output from ‘variable’ to ‘fixed’ - also go onto try switching it back to ‘variable’ and see if it will work on either type of audio output, but start with the HiFi volume set to say 50% - in case the Connect suddenly springs to life. 

Another thought is to re-seat it’s RCA cable at both ends, or better still, try another cable (if available).

If the PANASONIC is old enough it might have a Tape Monitor feature that will create the symptoms you are experiencing when accidentally engaged.

I liked the idea - but it didnt work :( I also checked it with another RCA - no luck either

I dont know about this feature, but I tried aux to play from other source - and it worked fine :(

(The Panasonic is approx 20 years old)

@Sinus,

You’ve tried a good many things without success so far, so I think your best bet might be to submit a Sonos diagnostic report with the Connect playing in the Sonos App. Make a note of the reference generated, and when practicable, contact/chat to Sonos Support Staff online about the matter via this LINK and see what they can see from the report. Here’s hoping it’s not a hardware issue.