I'm using push to talk. Seems to happen with chrome and spotify. I notice it especially when listening to music.
I'm on a windows 7 box with my sound->communications option set as "Reduce the volume of other sounds by 80%". Although I've found that this doesn't even affect mumble.
I also have tried sound->recording->microphone properties->advanced and unchecking both "Allow applications to take exclusive control of this device" and "Give exclusive mode applications priority"
I have audio output in mumble set as:
Attenuate applications by 0% as well as the two options UNchecked. (while other users talk / while you talk)
Any help is appreciated :D
No sound driver fancyness? (Volume gain, normalization, etc)