Engine Noise through stereo

What I find funny is that I had mega engine noise in my aftermarket stereo on my 1992 Olds Cutlass Coupe, but zero when I installed my new system in my Dart...go figure...LOL.

CD player
2 - Pioneer 6x9s
1 - JL 10W3V2 subwoofer
1 - Kenwood 1200w 5 channel amp