Sonic with a 496 engine noise
 

Z06 Sonic Port engine started making a noise on his last ride before leaving today. Clunking noise with engine rotation. Engine idles smooth, noise gets faster with engine RPM. Sounded like the back of the engine, you can hear the clanking through the air intake. Tried unplugging back plugs to alter noise, did not seem to change noise. My PQ had a similar noise when I had a piston problem. Any idea's to look for. I found my problem by removing plug and putting a scope down the cylinder. Just trying to give Wally a direction.
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Check the flappers in the exhaust. They might be metal to metal now. Does it go away above 2500 RPMs

He didn't want to run the RPM's up. If it was in exhaust would you be able to here thru the air intake? We did try to turn exhaust on and off to see if it would alter noise. It did not change the sound.

You could here it everywhere. How are they or it running?

That is the funny part. It was running great.

Just to be clear, this is a factory Merc 496 ?

Yes, standard fuel injection. Stock engine.

Corsa muffled tips ?

Yes

Have had a few of those where baffle just inside them start to break loose where the owners thought they broke the motor.

Hopefully you don't have this! Stock 496 MAG this past September, Motor started and ran with a similar noise.

When was the last time you changed the gimble bearing?

Just pull the drive and run boat on hose to see if noise is still there. 4 mins to pull the drive. Faster than booting up OSO forums.