I would suspect some other program from burning too many CPU cycles or thrashing on your hard drive. If it has worked for 6 months, and you havn't knowingly changed anything, somethig else is messing with the sound system.
Have you tried disabling system sounds?
I have a similar set up, running on a 500 M Hz P3 and I have no problems at all. So if your rig is faster, I would look beyond the software you are running.
There was a program I had to disable in Mandriva 2006 that caused a lot of problems. It was loaded by default. Did that a week after the original install, so I don't remember what it was called. I found reference to on http://mandrivausers.org/
Hope this helps.