XJRider.com

On my way back from http://www.roadamerica.com/ (vintage bike races) after 300 miles round trip I heard a gargle. It was while I was coasting at ~30mph going down hill my hands and back sore so I took both hands off the bike to stretch and that was when i heard a mechanical - metal sound that had a rhythm. It sound like it was coming from the center of the bike. I had just taken out my ear plugs once reaching the city. I am not sure I would have heard it with the ear plugs in. It last only a few seconds and sounded like it worked its self out.

Any Ideas?
Thanks