Did you check the settngs of your sound card?
Although, im thoughtful cause your problem fixed when you mute the sound by ''Q'' and then you open sound again. 
If it was a sounds card problem i think that you will always had it.if i was in your place i ll try to unistall the sound card and reinstal it.In case of you dont have a sound card and use the MOBO audio output try to unistall-install the sound drivers.
As an extreme solution i would also suggest to reinstal FS.I know that it is time-consuming and especially if you have add-ons etc. but if its a problem that starts form FS sounds is the only way to discover and,maybe,solve it.
Thats my opinion and im not talking as an expert.Just thoughts of the moment.
Stay on touch and let us know... 😉