Weird sound from MacBook Pro 2011

I have a weird sound that occasionally occurs from my Late 2011 13" MacBook Pro. The sound comes from the left side of the base, towards the hinge. The timing is random, usually when sitting by itself idle with the lid open. It has occured when the charging cable is both connected and disconnected. Performing a restart does not cause it to stop, it will continue thru the restart. Shutting down completely does shut it up, but it'll likely appear shortly after booting up. Closing the lid of the MBP will shut up the sound, and if left closed for a couple hours, the sound doesn't appear for awhile.

The sound itself is pretty loud, and can easily drown out my TV when it kicks in. I don't think it's the fan, as I've heard the fan on full tilt and it's still quiet, unlike this noise I am referring to. Plus, the fan is located in the center against the hinge, not on the left where the noise is coming from. I tried resetting the SMC and NVRAM, no luck. I did record the sound with my cell phone, here is a video of it:

http://www.youtube.com/watch?v=OgutF9bZilI

If anyone has an idea of what is causing this sound, please help. Thank you.