Is it possible to set a Nikon D7000 to release its shutter when it detects sound?

I'm trying to take a picture of a guitar string being played for a college project on harmonics. It's pretty difficult trying to take the shot and pluck the string so that it captures the shot as soon as I let go of the string. I'm aware that you can set up shutter release via sound detection with use of an external microphone but can I do this without and if so how?

Not without extra equipment.

Nice camera, but it can't do that without buying something extra.

You will either need to build one yourself, or you can get them already made, like this: http://www.pmgadgets.net/product_info.php?products_id=51