Before identifiying the LNB as the culprit, I changed the SDR radio (Adalm Pluto vs. RTL Dongle), the software (SDR Console vs SDR Angel, including the latest updates), the DC source and I checked the Bias-T. I even changed the cables. Only after trying the third LNB, I had a clear audio signal.
What puzzles me is that two (Bullseye and a standard consumer LNB) out of three LNBs in my sample generate scratchy signals. Therefore, I assume that this might not be an uncommon problem.
Is there anybody who observed a similar signal and behaviour? Is there a way to solve this problem? Could it still be a software problem? Configuration? Help and ideas are highly appreciated. The reason why I'm asking is that I would like to work with the Bullseye. The one which works is not stabilised, yet.
73 de Timo