Ampeg SVT 3 PRO crackling and popping

[Davis]

Hey everyone. I have had an ampeg SVT 3 PRO for about 4 years. I am noticing when I play that once and a while the signal crackles and pops then cuts out for about 30 seconds, then floats back for another few seconds then clips again. While it is crackling the peak LED is flashing. I have replaced all my tubes (they needed changing anyway) and the problem is still there. I noticed the amp is quite warm when this happens. The air blowing out of the vent is also quite warm.

I was thinking maybe some biasing needed to be done, but the signal generally sounds decent when its not crackling and popping. Ive spent too much time over the board pulling my hair out, and need another opinion. If anyone can offer some wisdom on this instensly annoying problem, that would be amazing!