car audio - engine noise

Hey guys. I have an aftermarket system consisting of a clarion deck, two jbl amps, and a crossover. Two pairs of RCA's running to the back... when i plug in the Monster Wire RCA's (a lot heavier shielding than my Stinger hyper series), i introduce engine noise into the system. And i do mean engine noise. When the deck is muted, it is so damn loud!!! On an unrelated note, i upgraded to a different amp, so i know it's not the amp that's doing it. My guesses are either the crossover or the RCA's... but this didn't happen in my RX7. There was absolutely no engine noise in the system at all, and i had the same exact components. Is there anything that i could inspect? Perhaps a bad ground somewhere? Where? Should i re-do the grounding for the alternator?

Thanks guys
-Ross