this is gonna sound odd. Go to the speaker wire that connects your amp to your subs. On the speaker terminal change your speaker wire, switch them. You know how pos is to pos and so on, switch them on one terminal if that doesnt work switch it on the other terminal. Sounds odd but it happened to me i brought my car to a car shop and all he did was switch the wires he said sometimes the frequencies throw eachother off. Didnt understand what he was saying but my system was thumping. Check out what i said and let me know. And if you have no clue what im talking about ill make a video just let me know.
yeah i only had to switch one set. My problem was with all the wires set up normal my subs werent hitting they were moving real soft. So i took it to the shop they switched the wire and it started hitting hard.
Blaine i only had to switch one. I dont know if we had the same problem, this was mine... When we installed everything my subs didnt hit. They were moving real slow n soft, so i took it to the car shop they switched the wires and it started hitting right away. I hope this helps.