So we have this old Peavey PA that we used to use with my old band for practice. Now me and my friend want to use it to practice with a new band, but it is having some problems. Being the DIY Electronics type of guy I am, I want to fix it myself. Here is the problem: If you tap the head with light amounts of force, it sounds like it is shorting out somewhere and makes a horrible and loud crack. It also does this if you are plugged in and playing with the head on top of the speakers. I opened it up, and I was able to determine the sounds are coming from the second of 2 circuit boards, which is the circuit for the power amp. So I started tapping around on the circuit board (with a drum stick) very lightly to see where it most easily made noise. (I know, cave-man electronics testing). it seams to make that loud crack most easily when I tap around/on these large capacitors, which is near the transformer. Has anyone heard of problems like this or what these problems could be coming from? Any help would be nice. and yes, I have a multimeter, I tested some things and everything I have tested looks good.