Had a noise problem and figured it down to the ground on the amp. So, I changed the ground and the noise went away.

Unfortunately, it came back after two weeks. Switched screws and added a lock washer. Went away...

Big surprise, three more weeks later and it's back (rough estimate of time)...

So, my questions:

Where is the best grounding point in a passenger car trunk that seems to have no support beams?

What is the best grounding hardware to use, screws, type, etc..?

Any other useful suggestions?

Before I got this car, I had a minivan, and boy, that thing had more steel grounding points than I would ever had needed....This car, it has nothing useful....

Thanks for the help.
-Steve