I just got a 5.1 surround sound home cinema system. The subwoofer has a great sound but there is a very annoying crackle coming from it at the same time. I have tried using a different subwoofer with the same impedance (3Ω) but the crackling persists... Does this mean the amp/DVD player is broken? Could it be the cable from the amp to the sub? What is "breaking-in" and does it have any relevance?