Sound like ta ta ta ta ta

I have a 17" PowerBook that I had monitor problems with so I brought another on E-Bay.
The new one had hard drive problems so I just exchanged it and all was fine except for a noise that sounds like paper in a fan. When you put it to sleep the noise will stop but then will start up again
when I adjust the sound. If the ear phones are in the sound is fine. What can be the problem, any help will be appreciated.
Randy