Audio distorts/poops out on Mac Pro - Advice needed

I have a 2009 8 Core Mac Pro w/12 GB RAM running OS 10.8.2. I've been trying to troubleshoot this problem for some time now. WIth just about any audio app - iTunes, Pandora, Spotify, Ableton Live etc. after a certain amount of time, the audio starts to distort and ultimately gets reduced to a series of repeating clicks. The only solution is to quit and restart the app which resolves the problem every time. I've switched up audio interfaces, switched up MIDI/USB cables. Tried plugging them into different ports, out of hubs and directly into my Mac. I thought it might be memory related, but it seems to happen when I have enough available memory as well. Happens in all audio apps. Any advice on how to troubleshoot?