Crackles and garbled audio for playback and sometimes record

When I’m playing back audio in cubase 8.5, it’s fine at first, but then starts to crackle slowly at first then gets worse until it’s pretty garbled. It starts almost like rain, like one small crackle then builds up and gets worse. Then it will go away after 30 secs and it’s fine. Sometimes it happens when I’m recording too, and when that happens I have to restart windows. I know it’s not the cpu as my meters aren’t moving past 1/3. Anybody have any idea what it could be?

THanks

Shaun