I have a chv 454 in my carra jet boat,it makes a noise at 2800 rpm to 3000 rpm like you put screwdriver in a fan blade.It will onley do this in the water.The motor runs grate the rest of the time. Need help.
the same thing happened to my 454 and it was a flat cam lobe and a few bent push rods. it would do it above 2500 rpm's and sounded horrible. sounds like its time for a rebuild.
Are you sure its not your fly wheel touching anything ? That has happened to me on past jet boats at certain RPMs