Anyone out there experience a similar problem?

I've got a noise coming from the drivers side rear door (super cab). When I hear the noise I can feel a vibration. It doesn't happen when the front door is open. It doesn't happen on every bump. A rolling/flexing of the cab conbined with a rough surface most often causes it to happen.

It's been in the shop twice and they can't seem to figure it out. They thought it might be the latch striker plate or the locking mechanisim rods or the trim pannel and one guy said it was the bed cover or body mounts. None of these things seem to have been the problem.

Any ideas?