Originally Posted by
Andrew R Stewart
AS you ride and can hear the noise try placing a finger on various parts to see if the noise changes. Like the casing (good suggestion by Francis) loops. Also make sure the valve stem base nuts are snug (or jus get rid of them). Andy.
Actually I was thinking of the bell clapper standing up above the FD about 1/8" from the seat tube.
The suggestion about stones stuck to the rear tire hitting the seat tube is also good.
In short the OP has to let go of the wheels and consider
every possibility. Often the actual sound is a valuable clue, but we can't hear that over the net.