Strange noise at low speed. Cavitation sound?

[SeptemberC]

I am aware that sounds are difficult to diagnose when you are physically there and almost impossible when you can't hear it yourself but here goes my attempt to describe it to you. . .

At low RPM 2500 going around 10 MPH or slightly less I am hearing a sound that resembles two pieces of metal maybe vibrating against each other. Like a shroud is loose and vibrating. With the engine cover up you can not hear it. You can only hear it with the sundeck down. Opening the ski storage area does not make the sound louder.
My intake grate does have one of the fingers bent to one side considerably. My thought was that this slight disterbance in the intake water was causing some kind of cavitation.
Your thoughts?

 

[Dr Honda]

cavitation, doesn't normally have a sound associated with it. It's basically, just air trapped in the pump, or a by-pass of the water... and then you lose thrust. But... since the pump isn't loaded properly... you can get sounds from the pump shaft, gears, or nozzle... if they are bouncing.


Since you asked about servicing the pump... I would be suspect of the gears... but if the noise goes away as the RPM's come up... that's probably not an issue. But, it's best to drain the oil, and see what it looks like.

when you hear that sound... and you push the throttle... does the boat accelerate?



Personally... I'd be looking for something loose... like the rear ladder, or other hardware.

 

[SeptemberC]

Ahhhh the ladder! Never thought to look at that.
After we change the fluids I'll let you know if we found anything else that could be the culprit.

 

[Dr Honda]

You will know REAL QUICK if there is gear/bearing issues... once you drain the oil. If there is a metallic look to it... things aren't happy.