Short "Bzt" noise

Hello

today my macbook pro started making a strange short "bzt" noise. It happens sporadically, and is about 2 seconds in length. Its a unibody from mid 2009, and has a SSD in it. It sounds like its coming from the top right-ish area. It doesn't seem to affect the operation of the machine.

My initial thought is it might be the fan not turning on. But the fan didn't run that much to begin with, and its happening when the machine is not hot, so I'm not sure.

Thoughts? Has anyone ever had this before?

Thanks!