knocking noise?

[jbh]

i have a 94 merc 350 mag and when i get it around 5000 rpms i hear an annoying knocking noise that comes and goes. anyone know what this is?

[Jetaholic]

Sounds like it might be detonation.

[Beer-30]

Is it pinging or knocking?
Pinging would be detonation. If it is a thump-thump knock, it could be as easy as a gimble bearing.

[uselessgrant]

or your double u-joint. see if it changes with trim position