sorry, i havent been on all weekend (i got a condo in winter park and went boarding all weekend)...

looks like you guys have narrowed it down very well...

one thing we always do to find sources of electrical problems with audio is slowly 'debuild' your system until you are back to the most basic possible (it can be a pain but it targets the problem exactly)....
it sounds like an antenna ground to me...our ant. is not powered, however, all ant. should have some source of ground... and depending on what they took apart..

my guess is that they disconnected the ground, then sprayed the car, then reconnected and its no longer making a good connection...if you can find where the ground is...you can either sand underneath of it or you can use a 'star washer' that cuts into the paint down to get a good ground...

try to find your ground and see if that helps...