I've noticed with any distribution I use, whether being Kubuntu (latest), Open SUSE 10 or Freespire 1.0 when ever the system plays a sound for an event such as a pop-up window, the volume can increase for no apparent reason at all. It'll start off at it's normal volume then increase at any point of the sound file.

So far this is the main reason I haven't done a switch to Linux from Windows for main desktop applications (except gaming) as these sound problems do my head in (I'm an audiophile so things like this really make a difference to my experience).

I have a Sound Blaster Audigy 2 ZS sound card which functions without problems under XP Pro, so I know this isn't a hardware issue.

I have an Audigy 2 ZS which I use under windows and under
Suse 10 with no problems. I wonder if the problem is with
your alsamixer configuration.