5.7 ltr whining / Humming noise

[Mark christy]

We have a 5.7 Mercruiser EFI with a Bravo III. 2000 model with 400 hrs. Runs beautifully but approx 20 seconds after start up a humming or whining sound emerges. Not loud but noticeable, doesn’t have to be in gear.
Increases with the revs and easily heard at WOT but doesn’t drown engine noise out.
Have run engine without serpentine belt but noise still there. Have crawled down the rear of engine and really sounds like coming from the rear drive somewhere?
Anyone got any idea?

 

[Scott06]

Check gimbal bearing And u joints . While doing that run it with drive off , my guess would be gimbal bearing or upper drive gear or bearing noise.

 

[Scott Danforth]

Additionally, check the power steering fluid level

 

[Mark christy]

Thanks Guys, next lift we'll be dropping the drive off and have a look. Power steering fluid all good.