I am fighting a ground loop problem that is kicking my butt, I just can't get it fixed.

Where are you guys grounding your after-market amps? I have two hifonics amps in the trunk and I have the grounds both run below the spare tire location on the screw post (north of the battery). It seems as if there already was a black ground cable run to that location (factory).

Here is a picture of the install, I wish it sounded as good as it looked. It's been unplugged since November because I can't tolerate acceleration whine and I would rather listen to nothing at all.