Amp is thumping
hello. I have a hifonics Brutus 2400 mono amp hooked up to 2 DD 12's. they have been installed for a few years. All of a sudden the subs stat thumping like a heart beat. So I have determined this only happens when car is running. I turn the car to acc mode and I can play it for as long as I want and it's fine. But once I start the car it starts thumping within 30 seconds. I have a scorcher line out converter with remote. I need to keep stock radio for all the functions in the car. So I tapped into the rear door speaker wires, go to the LOC. Then an rca from loc to the amp. With the loc remote powering on the amp. Even when I remove the rca from amp, so only the remote ground and power are the only inputs I still get this issue. The ground wire is tight and bolted to the cars frame. Speaker and power wires are on opposite sides of car. Again this happened out of no where. Could it be the LOC or amp? I don't think it's the amp due to it plays just fine without car running. Any help would be appreciated. Also when keeping stock head units, is a LOC still the best solution for hooking up amp?