i need a little help.i just installed a nice 12 subwoofer in the trunk with an amp.the problem is every now and then all the sudden the volume will jump up really loud.then about 5 seconds later go back to normal.its really anoying and scares the crap out of me.this only started AFTER the install with the sub and amp.i still have the factory deck in there.am i doing something wrong?id really appreciate the help.thank you in advance..PS this is on a 2000 S500