Strange grumbling noise behind engine

[BERK30]

I am having a weird noise coming from below deck behind my engine from about 2100-2400rpm. It’s a deep, loud grumbling that’s coming from behind the engine (yanmar 3YM20). The noise is rpm dependent, and it happens in forward, reverse, and neutral. 3000 rpm cruise, I don’t hear it at all. Noise can be heard from 1900-2600, but from 2100-2400 it’s REALLY loud. 90 hours on the engine. Maybe 15 of those hours put on this season. Does anyone have any insight to what this noise might be? I took a video from the front of the engine, which sounds more or less normal. The second video shows the noise coming from the rear. Sounds like it might. E coming from below deck. Thanks!

 

[odaydokay]

It sounds a bit like something I had a few years ago, and it turned out to be a cutlass bearing. We limped home for about an hour and maybe I could’ve gone a bit longer, but I got her attended to right away. I meant to add that I dove under the boat and gave the prop shaft a good lateral wiggle. That produced a similar noise, and there was play that should not have been.