My new system has developed a very slight ticking noise. It's not a whine, it sounds like a taser, but much quiter. It's mostly from the rear speakers, but is present in the fronts to a lesser extent. And of course, I can only hear it while the motor is running. It's quiet enough it doesn't affect the sound, I can just hear it if I turn my head right.

I'm pretty sure it is ground loop noise... However, I don't believe this noise wasn't there before the amp went in.

Should I add a ground loop isolator or try simply grounding the HU case?

System...
Aiwa CDC-X217
Pioneer 6.5's off HU
Alpine MRP-M500
MTX subs
8 gauge power to amp along driver side with 8 gauge ground to clean body bolt
2 x 8 gauge battery ground cables
6 gauge body to engine
Shielded home theater RCA's running along passenger side