Sorry for my delayed answer.
no that was the firsth what duble check too.
The background musik feature its not the issue.
The noice issue comes from the duplex amp, its a hardware bug.

The noise its Similar too a cheap old pc soundsystem, when no signal input was active, always noice was present.

i have replace with newer smt-i6011, its fine and mute.

I check in a similar enviroment by a good customer, its the same.
I'm sure nobody hears it in everyday life.