What he said. Screw loose inside the case is one of the worst things that can happen to an empeg. There have been people who've completely ruined their units because they kept playing them even with the loose screw. If you short the wrong two contact points with a screw, the expensive blue smoke can be permanently let out of the player.
Make sure it really is a
loose screw and not just the standard disk rattle, though. A loose screw should be unmistakable.
Popping noises could be related to loose screw, they could indicate hard disk trouble, they could indicate wires loose on the docking connector, or even a bad amplifier. Check
each of these things.