Possible Answer
I noticed this thread being an older thread but since it was never resolved I might be able to contribute. This morning I noticed my MBP rattling a little. It wasn't severe but enough to catch my attention. It only rattled at certain positions. Initially I thought it might be normal except that I'd never heard it prior to. I made a Genius appointment for this afternoon & took it in. I was afraid the genius would give me some bull about it being normal or even that they couldn't hear it. Fortunately I got a competent genius (unlike the poor sap sitting next to me) & he & another genius took it in the back & confirmed the rattle. They explained to me that it was a loose metal component/tab associated with the optical drive. He told me it wouldn't likely hurt anything to leave it but since I was still under warranty it might be smart to have it repaired. Sooo needless to say I am MBP- less for a couple of days but hopefully the issue is resolved.