sub goes crazy for a couple seconds... amp into protect... suggestions?

checked the power and ground... its steady, plus my highs amp is off the same distro block one foot away and that amp is perfectly fine. Pulled the sub, Dual 4ohm coils read 3.9 on each coil, checked and double checked all my wiring, it all seems fine, the only thing i haven't gone through is the signal wire itself... is it possible for a short or a bad signal wire to cause this problem?

symptom: turn the car on plays fine for a minute, then a couple really loud pops and protect