There is also noise on my unit. Just after switching on it is ok, it comes later and it does not depend on the source.

Unfortunately, this also happened to me. Strangely, practically inaudible at the beginning (after switching on), but clearly audible after a short time.

Yes, there is a basic noise (white noise) of the amplifier, which is constantly audible up to volume 7 or during very quiet passages. This is often the case with units in this price range, so it is not a malfunction.

nothing detected so far - in daily use. on all sources or only one? if you move the unit, do you still have the problem?
either something in the device / amplifier / unclean signal or external source of interference.