Mercury 175 1997 noise Help!!

[Moto x]

Anyone have any insight on this noise. Started the other day out of nowhere and only happens around 3500 ish rpm at a low engine load. As soon as you tip into the throttle or back off nosie goes away. Sounds loudest by the stator end of the engine. And possibly carb side of the engine. When my hand is in the throttle linkage at the carbs reving the engine I feel as if I can actually feel a vibration that matches the frequency of the noise. Does it in gear or in neutral. On the hose or in the water Doesn't matter.

Here is the video, the noise comes and goes as the rpms change.

 

[Moto x]

I'll add when I spin it over by hand I notice no rough spots that I can feel by hand.

 

[jimmbo]

Welcome to iboats

Sounds like a High Speed Miss.
Inspect all the Plugs, Wires, and Connections.
Drain carbs, looking for water, dirt in the drainings
When you are 'revving' the engine, are you advancing the timing, or are you moving the throttle shafts?
And it doesn't do it under load, as in, In Gear, using the Throttle Lever?
Any work done to the Engine prior to this occurring?

 

[Moto x]

Cruising at a consistent speed and right around 3500 rpm noise is there. But if I tip on or off the throttle to up or lessen the load noise goes away. I would say it does it at 30% load area. don't notice any performance changes so I don't think it's a misfire. No work done to it recently. I believe when I'm reving the engine I'm thinking I'm on the throttle shaft at the carbs.