Was noodling around last night with my guitar, then picked up my iPhone 5s to check a message I got and this happened...
[VIDEO]http://www.youtube.com/watch?v=mILLiCRltkw]Weird iPhone 5s Fingerprint Reader Sound - YouTube[/VIDEO]
The noise was coming from my amp. Clearly a grounding issue or something. Not sure, but it scared the fuck out of me when it happened the first time.
That is your fingerprint being sent to NSA and running it's daily database checks against any newly acquired evidence.