Well, we've done these cold bike chirping noises with nothing rolling or revving (non-belt, non-engine noise) before and the very best (funniest) of the lot had to be the Atomic Cricket.
If your noise stops when your pipe gets hot, look to your bracket, mount bolts, header nuts etc before you get the flashlight and start to looking up inside the muffler for the little mutated nuclear cricket what has moved into your muffler to stay warm ....
(broken baffle inside the muffler rubbing while cold, expands when hot and the noise stops)
If you can catch that Atomic Cricket you can sell him on Ebay for thousands of dollars .....