What kind of guitar are you playing? SIngle coil pick-ups are a lot noisier than humbuckers. Also gobs of gain will make any noise louder, and the closer you are to the amp the noisier it's gonna be.
Suppose I should have asked what kind of noise it is. Try unplugging the guitar cable from the amp and see how noisy the amp is. This will give you an idea whether the noise is from the guitar or amp.