HI I have a engine noise coming for my speakers. Can someone help me fix the problem. I'm running memphis mclass 5 1/4 front speakers and mclass 6x9 rear speakers and a memphis mclass 75x4 amp to the speakers. I have jl 4 channel blue rca to the amp. I get the noise if the head unit is on or off.When the head unit is off the amp is off.What can my problem be.