Just for the record: the noise is actually a result of the mainline kernel powering down the audio subsystem when not in use. Disabling this as described in the below quoted post works also with my Banana Pi. With using a cable (as described above) the noise is gone, but still there is quite a loud "plop" when the audio-subsystem changes its power-state. Disabling the powering down of the audio subsystem removes also the "plop" - so I removed my cable.... and the "plop" :-) Cheers, Be