What is this sound on Mercruiser 4.3, Alpha One?

[larryarnaud]

I have a rattle that is coming from somewhere around the bell housing. It only is there during idle. It goes away when throttling it, even just pushing a little on the throttle. Here's the sound:

 

[alldodge]

Plug wire arcing, exhaust flapper, maybe flywheel dust shield is loose

 

[nola mike]

Sounds like the exhaust flappers to me.

 

[Lou C]

best way to tell is get a mechanic's stethoscope, I found a noise using mine that sounded like an engine knock coming from a rubber covered flapper on my Cobra...drove me crazy after my top end rebuild till I found it.....thing was I had to change to a different exhaust design at the same time (OMC one piece batwing to 2 piece manifold/elbow) which I guess changed how the water flows into the Y pipe....

 

[QBhoy]

Sounds too tinny to be a flapper and not routine enough to be something mechanical and steady...sounds more like a loose bracket or rattle

 

[Lou C]

Perhaps that tin cover over the bottom of the flywheel housing is loose & vibrating…