Sounds like a cracker fly wheel to me.

Is that different from negro flywheel?

Sorry couldn't resist

Sounds like internal exhaust tip flapper to me. Put your hand on the tailpipe hose near the transom.
Does it go away with some rpm?? Flapper noise will go away with with a few hundred more rpms.

Yes. Way different. Lol!

Negro flywheel would be a lot larger, right? ;)

My boat has developed what I would describe as a "chirp" coming from the exhaust, but it is a steady sound that seems to be in time with the firing order. Ran a compression test the other night and all were at around 180 - 185 psi. Some OSO'ers have said that it might be a loose baffle in the exhaust muffler. Planning to try some different muffled tips to see if it changes any. Good luck with yours.

stick broom handles up the transom exhaust to keep the internal flappers open while running the engine - this will rule in or out if thats your noise. Process of elimination the start of it

pull tips / mufflers shake the hell out of them by hand --- Noise ??? run engine however without the tips / mufflers installed ---- Noise ???

A real doctor stethoscope will find this noise in about 15 seconds. Use one all the time best tool to have for marine noises hands down.

Were you at Cumberland Thunder Run???

There was a boat in my fleet that had a chirp noise from exhaust. ...and somehow I got behind him at each stop. That chirping noise was driving me crazy!! LOL

My vote is an exhaust flapper. Does the noise change or go away with a little rpm?

No not really , I took the recirculating pump / alternator belt off and it seemed to go away but the engine got louder (threw me off a bit) but I think the RPM's just went up because of the belt being off . So I think it's the alternator or the recirc pump and I will try eliminating the flappers as a possibility as well