Had tried changing frequencies and bit rates already. No change after that.
I am not using wireless headsets. I have musical stereo monitors, a wired gaming headset and Hifi-Headphones.
Interesting enough, after the last game start without change in setup or configuratioon and even without restarting the machine, the sound issues were gone. I am trying to remember, what else I had changed in between. I have played a round of Star Citizen. Then I have installed "The Battle of Jakku". Maybe there came a fix with it.