my amp (fender M-80 2x12 combo) has been giving me a problem as of late, when I turn it on and turn up the volume I can hear it being turned up but it has a REALLY distant sound, but if you tap it on the top(above the EQ housing) a few times the noise level jumps back to normal and then it starts to play fine, but every now and then the noise will decide to crap out and I have to tap it again to get it back to regular volume.......so any suggestions on what the fucks going on?