Oops. I think that volume switch is kind of a touchy, fragile area from the posts I read. Here's the rubber piece post; I guess it isn't super critical:
http://forum.ppcgeeks.com/showthread.php?t=31680&page=2
Seems like alot of ppl are taking theirs apart. Hope you get it back.
Edit: In the "Reassembly" from that take apart post
When reinserting the main-board there is a little rubber piece on the bottom that falls off. Make sure that's still on there when you put it in. Seat the botttom at an angle. Then make sure the volume control button is lined up with the black tab on the mainboard. If it's not lined up you'll break this tab off when you try to change the volume. That is bad.