Speakers (or computer) dying?

So every once in a while, I lag (in both MS and Firefox). When I lag, my sound gets REALLY choppy, slows down, etc. I CCleaner'd my registry, thinking it might be a registry error or something, and checked to make sure none of my audio files are corrupt, but it still happens. Also, my computer is experiencing some slowdowns, especially at startup.

I haven't virus/spyware scanned in a while, so I'll do that tonight while I'm in bed, but I need some other suggestions if that doesn't help. :[