I'm running 2 SWS-12D4's with a Pioneer T5200 (bridged) in a sealed box in my 2012 Mustang. These subs hit pretty hard, but I've noticed that if I roll down the windows, or pop the trunk with the system on, these puppies THUMP!! Is this normal? I have the whole rear deck and trunk covered in Hushmat, which has nearly eliminated any rattles. Any thoughts?