MacBook Pro :: Moving Or Tapping Weird Sound

When I pick it up, or when I move is suddenly (even just slightly), I get a horrible sound from the back right hand side. It sounds like a someone is putting a piece of plastic into a spinning fan. It also kinda sounds like the hard drive head hitting the disk (scratching sound). I know that these things are meant to have a movement sensor which actually takes the head OFF the disk, but this sounds like its doing the opposite (scratching the moving disk). If I do it while watching a movie, the film freezes for a second at the same time the sound can be heard - so it's definately something to do with the hard drive.

I have done some research but everyone talking about the sudden movement sensor has described the sound as a "click", not a scratch. Can someone confirm this is normal, or abnormal? It's happening quite a lot - e.g. if I just pick it up it occurs. I've had loads of laptops and this is the first that seems to make a sound whenever I move it...