Hmmm... the repair side of this kind of stuff can get dicey, and certainly isn't my forte, either.
I'm pretty much following your line of thinking, though. It does sound like a loose connection of some sort, or possibly a partially damaged component (maybe to do with the power source?).
Since you're out of warranty (I assume), I guess it wouldn't hurt to take it to an electronics repair boutique type store and ask for a free estimate. Or maybe just talk with an expert on the phone/over email before going out of your way.
Then, there's always avsforums.com. Though it's a bit of a labyrinth of information and at times bickering over there, asking the right questions can lead to great insight. They still have many knowledgeable posters.
I hate steering people away from this forum, but this is somewhat specialized. Wish I could've been of more help.
__________________
|