Radio picking up interfarnce from truck engine?

i installed a system into my 1991 f150 with a in-line 6 and 5 speed manual tranny its a 800 watt sony amy hooked up to a 800 watt kicker sub everytime i connect the silver grey scorch audio wire the sub plays a beat form the engine rpms and radio at the same time i have no idea how to fix it any ideas thanks.