Amp crackling?

[Mvaladao]

I have an ampeg SVT 450 head with a matching ampeg 450 cab.
I brought it back home after band practice and plugged it in. But when I turned it on to play it started crackling randomly. At first really loud, but over time it got softer and now it's pretty much one. But every once in a wile I'll here a little crackle or two.

Has anyone ever had this happen to them before? Or know what this might be from?
I have it plugged in to a PA system, maybe that might have caused it to start this?

 

[craig.p]

Can you make it crackle when you smack it? If so, could be a loose internal connection, maybe a cracked etch (trace) on a circuit board. Also try connecting the effects send and return with an instrument cable (could be one of those jacks doing something strange). Those aren't all the possibilities but let's start there.

This head didn't take a physical jolt coming back to your place, did it?

 

[Phalex]

Could be a dirty pot. Does it make noise when you twist a knob?

 

[Lazarus.Bird]

I had an SVT-3 that made some weird static crackling noise because of a bad input jack and it didn't matter if a cable was actually plugged in or not. When you plug a cable in does it lock in well?

 

[Vakmere]

Look for Rice Crispies in or near the transformer.