Update - ran it again a couple weeks ago on the hose while winterizing, and took some more video from back of boat. Finally managed to get the file to upload. You can hear the "squeak" that seems to be in time with one cylinder. I was thinking about pulling plug wires to see if it goes away and locates the cylinder that is making the sound. Is it OK to do this with a T-bolt IV? I thought I read somewhere that you shouldn't do that with Merc ignition, but maybe that was with the newer MPI boats.

Let me know what you think. Haven't had time to do compression check or leakdown. If I'm still worried about it after this I might just pull the heads and check everything out. Head studs with Cometics that can be used again, so only thing it would cost me is time and a set of intake gaskets.

Problem with pulling a wire off while on the hose is reversion.

But yeh, with my ****ty computer sound I can definately here the squeek. Pretty loud.

How low is your idle rpm in that vid ?

Before I even considered pulling the heads I would yank those muffled tips off and run a set of straight tips to see if that eliminates the noise.

Good call ! I didn't really look !

A friends 28 Donzi ZX had a rattle that turned into a squeek- loud ! The baffle inside the driver side Corsa tip busted loose and was damn near blocking the exhaust air path.

Sounds like a weird exhaust leak type of noise to me. Hard to tell over the interweb. I agree with Matt, I'd be removing those mufflers before anything.

I always re-torque my header gaskets after the 1st heat cycle. Especially running aluminum heads. Is this a flat or roller tappet cam? If it was mine I'd re-torque the exhaust manifolds. while it's hot and running. If the chirp persists I'd pull the valve covers and check the rocker adjustment and look for a loose rocker arm.

Sounds like you are down a cylinder on the odd bank.

by watching those exhaust flaps,,I say the even bank is missing a pulse.w/ it running try to feel the bottom of the exhaust manifold by the exhaust port,feel for a cylinder making no heat.

OCCJoe (member on here) his boat has the same chirp to it at idle, maybe even louder. I personally think that it sounds good as long as everything mechanically checks out.
I talked to him at a poker run about how the boat sounded unique, he said he thought it was due to the heads. I think he has AFR heads

Infrared heat guns are pretty cheap and will help troubleshooting a dead hole a lot more effectively than pulling sparkplug wires. I just replaced my Corsa mufflers with straight through tips with the rubber internal flaps and thought that my motor was coming apart, so an exhaust issue is an easy problem to check. If something is broke in the exhaust tip that may give the irregular exhaust pulse as well and you can investigate that while it's winterized. Otherwise I'd get a heat gun and start shooting it the exhaust primaries.