I just wanted to bump this thread as I've recently had this issue with a 2013 15" Retina Macbook Pro. Switching off the automatic graphic switching would fix the problem but kill battery life. I was a bit upset.
Did the SMC reset and wasn't very optimistic about that being a possible fix, but it seems to have worked so far. Automatic graphics switching is on and I seem to have a clean audio feed where before I didn't.
Hope this helps.