Does it do it as you slow down? try letting it slow down gradually with out using the front or back brakes.
Listen to it and see if you can tell front or back.
If you have changed to a chain that has eliminated one thing.
Air filter... might have given you the problem
Exhaust even though not leaking might be compressed enough that a larger baffle would give it a chirp, if your baffles are small then I doubt its the exhaust.
My reason for the slow down without brake is rotor warp... highly unlikely, but narrows your chirp down.
Does it only chirp under torque? or can you produce it without getting it in gear?
Just some thoughts for you to try...