I get a similar noise coming from the right side of the laptop when I pick it up sometimes. I notice it the most if I pick up the laptop with one hand and it doesn't stay level. I haven't had any problems with my MPB yet though. (2011 13 inch).
I haven't opened up the laptop to investigate, but I suspect it may be the DVD drive. Or possibly the hard drive (I hope not).
To anyone else who may know what this noise is, is this something to be concerned about? Should myself and the OP take our MPBs back to Apple for repairs?