Sound volume fluctuates

[localz]

Since a month or two back, my sound volume starts to fluctuate from high to low and vice versa. I've not messed with it or anything. This happens whenever I play games, listen to music, and watch dvd's. When I first got the computer it didn't do this but all of a sudden this is happening. My computer is a dell dimension 8300 with soundblaster audigy. Please someone help. Thank You