Are my RCA Cables bad if...?

I installed 4 alpine type r 6.5's running off a 4 channel amp. They had so much distortion (alternator whine when I accelerate and dead static) I was about to drive my pathfinder off of a cliff. I spent hours doing this and that and could not figure out the problem. So I was hooking the RCA's in from the back of my headunit and I missed the input guide on the back of the HU. My RCA cable just touched the outside of the plug in and it completely took all the distortion away. So I hooked it in properly and it still sounded like ****. I grabbed an old video rca cable for a tv and cut the actual rca tip off and electrical taped that ***** on there so it was touching the guides and it took all the sound distortion away. My question is what is the real problem to this distortion and how do I fix it the proper way instead of n word rigging it?