Not trying to say you didn't already check this but are you sure its not a fan a dvd drive causing this sound?
In any case I would check the smart data and I suppose run a chkdsk on the drive at the very least.
I'd see about getting it replaced via warranty even though lifeguard says its fine. Grinding noises aren't good to say the least.
I did take the side panel off to try and locate the sound and I'm sure it's coming from the hard drive! I'll power my machine down, unplug the hard drive and turn it on without just to be sure though.
LifeGuard tool shows 'PASS' next to the SMART status! I'll run a chkdsk now though!
Thanks for your reply!