I had installed on my cadillac seville a sony exploid stereo with two 12" JL audio sub powered by a 4 channels rockford fosgate 600w amplifier and the sound was decent and really clear, but I just bought my Jensen vm9311 DVD player and a new 2 channels hifonics (1200watts) amp for my other speakers, well what I was trying to do was switching those amps and use the hifonics with my subwoofer and the rockford fosgate for the rest of the speakers now it sounds way louder but the problem is that I can heard an engine feedback noise in my front speakers did i do something wrong? or there is something to do with my new stereo please somebody help me!!