Video hangs and then catches up to audio, every 20 mins on the dot

I'll be watching a video and every 20 minutes exactly the video will hang briefly and then speed up to catch up to the audio. It does this with everything from 1080p dtshd-ma mkv files, to streaming youtube videos. I've read through multiple threads and have changed every setting with still the same result. I then looked into it being caused by something in Windows, changing all the different Power Options and logging processes hoping to see a pattern when this occurs, with no success.

Best I can remember, I believe it started happening when bit-streaming became available and I enabled WASAPI audio but I'm not sure.

I am using XBMC on a Win 7 32-bit OS, and through an ATI Radeon HD 5450.

Anyone else had this problem?