Why does my guitar amp start making a crunchy/static sound when I play it?

I have a Peavey Rage 158 transtube series and I play it with a Boss DS-1 pedal. Everytime I play a note you hear a crunchy and static sound mixed. It's not distortion because it didn't sound like that before. Also it overheats very quickly. Can anyone tell me how to fix this problem?