nasty popping

Strange and scarry,

First I plug preamp, then poweramp, wait about 15 seconds with no volume at all and then strong popping came out from speakers twice and then stopped. I'm afraid if this will continue I will blow my speakers.

I suspect on preamp, cause I checked poweramp and it's ok

 

I will try,

preamp, compressor and poweramp (on bridge mode) are connecting with xlr cables, ground-lift knob on preamp and compressor was setting on "lift", connection between poweramp and box is 1/4". When I connect poweramp on box without any connections with preamp, everything is ok. I didn't try preamp only yet, but I will , so it's the reason that I suspect on preamp or even compressor more than poweramp