this was my problem , Caused severe crackling . problem solved . I had over tightened the screw on the amp and it went through the plastic beneath it and settled a hair away from the casing of the amp , and when the bass shook the amp too much it caused the screw to get close enough to the amp casing for current to arc across the gap , but only on the downward cycle of the vibration ,which explains why it only happend with subs at high volumes , good news , every thing survived undammaged .

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premier prs 880
focal k2p upgraded 6.5,s
tn52 tweets
2 jl 300/2,s
jl 500/1
2jl w7 8"s
tuned to 30 hz