Can anyone help me with this noise?
 

I have a noise coming from my 496...pulled the drive and there is no change. It's hard to pin point roughly where it's coming from. This morning on the hose it was faintly there at idle and wouldnt do it when i revved it...then I took it for an hour long sail...brought it back to flush it out on the hose and that is when I took this video of the sound....
https://youtu.be/r7tGtO_nQi0

Sounds like low tone whistle or hum created by air suction. Maybe IAC muffler

I thought that as well so I changed the iac and iac muffler but no change

I found two loose motor mounts today.. opposite corners. I noticed a small gap between the washers on the transom plate and the bell housing. Tried to tighten it but it just kept turning. Nut was stripped. Would it be hard on the coupler? and any chance of that being the source of the sound or something wore because of the loose mounts?

Hard to believe I'm the first one with this noise. Seems louder behind the motor.

Loose motor mount will wipe out a coupler. If one of them was on the rear, then it could be the nut fell out of the the transom plate

check to make sure your starter gear is releasing once engine is started ? I would check this first and foremost -- then make sure your starter / starter bolts are not loose either.

How easy or hard was it to pull away your outdrive from the helmet ?

Whats your engine alignment like ? Do have an quality alignment tool ?

Loose flywheel ? or an issue with it ? Loose coupler ?

Would not rule out a nut / bolt rolling around from coupler and or flywheel. or either of them loose.

Ok thanks for the suggestions. It was a rear mount that came loose, the nut stripped out but got the old one. I will check the starter out. I have an alignment tool off eBay but cannot remember which one it is. The outdrive seems to come off easy. When putting on the last 1/2 inch is a little tight it seems but thought it might have just been the o rings. Last time I check alignment there was more spline marks on the top of the tool but didn't seem off very much at all. Something loose and rubbing on the bell housing seems very possible. Was going to pull the motor for winter anyways so maybe I will do it a little earlier then I wanted to

Hooked a scan tool up to it today because the last few times I have use it i had a double beep with the key on but would clear it self after a little run time.
15 - map sensor circuit
40 - manifold / intake
75 - fuel level 1 Ci
77 - camshaft sensor....said 40% power and said it happend at mid 400 rpm. But I don't remember any warning beeps while running or reduction in power since I have had the boat.