Those little devils can be obvious (loose hardware, bad string) or hard to find (sympathetic vibration in a loose brace).... but whatever the source, here's a great place to start the search. Go to www.frets.com (Frank's sister site), go to the "items for luthiers" section and find the "buzz diagnosis" page.... and the eventual answer will be there.
First just try changing the string. Then check the nut and make sure the slot for the string is cut at the right angle to the peg or not larger on the peg head side then the fingerboard side. Sometimes when the angle is wrong or the string is tight in one part of the slot and loss in another part of the slot you'll get a clanging sound.
Antionio, I figured you were kidding but I had a vision of someone new starting up a thread about what a great luthier Frank's sister must be to make a site like Frets.com.
My imagination says that Frank's Sister's site would be an Arts and Crafts for the home sort of thing. I imagine that she would have a page dedicated to all the kitchen utensils her brother 'transferred" to the garage to make tools when he was a kid.
Ned, do you imagine Frank has ever been a kid? It's like to imagine Hogwarts' head teacher - Albus Dumbledore - as a cheerleader!!! And he have no tools! He does everything he does on guitars just with his pocket knife! I'd like to be Harry Potter, to learn from such a master!