your correct it probably is interference from the wires, they do sell capacitors or isolator at your local auto parts store and or stereo shop. just ask and or tell someone there whats going on and they can help you with it, this usually occurs on older domestic auto's when doing a serious stereo upgrade and is fixed by adding a capacitor or isolator externally to your alt. but since it's possibly due to your wires i think they can sell you one to mount close or on your distributor, also i know some high dollar wires come with grounding straps on them that could have something to do with this. (mine are msd and "do not" have ground wires)