Strange sound from an unknown location

[Val V]

After the engine was rebuilt and put back in the boat I am hearing this strange wroom wroom sound that seem to change with RPMs. Took below video with my cell phone but you can still hear it pretty clearly. Video is exactly 1 minute long. Would greatly appreciate if someone could give any clues as to where the sound could be coming from.

https://www.youtube.com/watch?v=nQiyscOb4jA&list=UUDokQ6bk4xTJif-h-uYz7Ug&index=1

[Dave Neptune]

Sounds OK

Val, sounds pretty normal to me. I didn't hear anything that sounded bad, just normal engine noises.

What are you hearing that worries you? You can isolate the noise using a screwdriver (plasticor wood end in your ear) and placing the tip in various places around the engine. May be alt noise you are hearing to.

Dave Neptune

[Val V]

Val, sounds pretty normal to me. I didn't hear anything that sounded bad, just normal engine noises.

What are you hearing that worries you? You can isolate the noise using a screwdriver (plasticor wood end in your ear) and placing the tip in various places around the engine. May be alt noise you are hearing to.

Dave Neptune

Thanks Dave for taking the time to watch it. You can hear the most of that sound I was referring to at 50 seconds on the video. The best way I could describe it is wroom wroom.

[Marian Claire]

Was the boat in gear or in neutral? Dan S/V Marian Claire

[Val V]

Was the boat in gear or in neutral? Dan S/V Marian Claire

It was in neutral

[JOHN COOKSON]

I hear a loping sound in the last ~ 10 seconds of the video the sigifiance of which I do not know.

TRUE GRIT

[Mo]

I looked at the earlier portion of the video and can't tell if your shaft is spinning...I was thinking it was not and truly is in neutral. Not sure if I hear something there or not but you could try removing the alternator belt and see if it goes away...might be accessory drive or alternator itself.

[Val V]

I looked at the earlier portion of the video and can't tell if your shaft is spinning...I was thinking it was not and truly is in neutral. Not sure if I hear something there or not but you could try removing the alternator belt and see if it goes away...might be accessory drive or alternator itself.

Its definitely not the alternator because I just put it in a week ago and the sound was there before it. It seem to be coming more from the flywheel side but sound echoes inside the engine compartment and it could be misleading.

I will try mechanics stethoscope that I have somewhere.

Edit: It was not in gear. Dont think the shaft was spinning.

[Mo]

Try holding a piece of wood to the accessory drive pully as the engine is running. About a foot or so long and just put some pressure against the pulley and the belt turns it....if the sound changes it's there in the accessory drive. The more I listen to it is sounds like an alternator bearing....

Not much help, I know

[67c&ccorv]

I heard "resonance" which I would gather is the reflected sound caused by the configuration of the engine room and vibration.