496 knocking noise
 

2003 496 mag with bravo drive,got a knocking noise around 4000rpm.Iam a gm tech so I know what a rod knock sounds like,this not the same noise,It almost sounds like your anghor is at the bottom of the bilge bounching around,engine runs great with good oil pressure,plenty off power so the knock sensor is not picking up any sound and not retarding timing.try it with the silent choice on and off knocking noise is there at around 4000rpm both ways so I dont think its a exhaust shutter,there is also no rethum to the noise
I can take over 4000rpm in neutral and it wont do it,the boat comes out of the water good so i dont think its the outdrive,
any ideas?Im lost.

thanks.

Piston slap ...gm was famous for that a few years back ....maybe a collapsed piston skirt ...

mrfixxall
 

Gimball bearing or a u-joint in the drive line.. does it get worse when you turn the wheel? had a bravo last week making a knoxking noise,turned out to be a gimball bearing...mofo to get out too,i had to cut it out..