Louder Music with Acceleration

I recently purchased a 2001 Chevy Malibu and while driving it realized that the faster I went the louder my music would get. At first I thought it might just be that I was charging and playing my Ipod at the same time, but after unplugging the charger part I realized its still doing it.
Any ideas what it could be?

Thanks in advance!

There is a ring type of knob behind your volume button that pumps up the volume" 80's flashback" with acceleration. Turning it all the way down will turn off the feature.

SCV speed controlled volume, its normal! :)

Yeah, I hated that feature as well. You can easily turn it off by pressing one of the buttons right next to the power knob. Cycle through until you reach "off."

I didn't mind it. I don't have it now since I beefed up my sound system. I kind of miss it. For some reason my passenger side door speaker always blows. The other ones never do. I must have replaced it 5 times now. It would go out even with the completely stock system. Damn teh electrical gremlins.

You have to give it to them. It's quite the little invention. Though it may not work precisely right every time, you have to admit it's rather smart.