Does the sound go away when you turn the volumes down? If so check solder on the input jack.
Is the amp putting out DC voltage? Measure at the speaker terminals. If so, you have a problem in the amplifier section of the amp- shorted output devices or the like.
Is the sound AC voltage? If so I'd check the solder connections on your filter caps and or check the caps themselves. Possibly one is bad.
It's a start.