I only suggested that because it sounds like it's getting worse. I would not suggest playing with the ground wires as that is something which should be done with the installer present. However, if he can hook up a home theater system I do believe he should be more than capable of undoing a set of tweeters and covering the wire ends to prevent a short. This should help the setup from killing itself from the most likely source of trouble. I think he's also more than capable of making the decision of whether or not to do this if the tweeters are installed a bit more complex than I seem to be imagining at the moment. If he can't figure out how to get the thing off the dash and remove the wires, then yeah, leave it alone.

If I installed a system for someone and it had a problem that was getting worse, I would certainly set the guy up with someone who could help asap if I couldn't get to it myself, especially if he had scheduled time to come in.