YO-EL

From last August:

Bad water pump bearings?

LoneStarFRC

Wow, noises and/or strange sounds can be some of the hardest things to pin down, not mention trying to describe them to someone. Posting your video should really help in that regard.

From your description and the your vid, it appears to be tied directly to engine rotation, and obviously of very short duration after engine shutoff.

The obvious things to me to check would be water pump (as you said), but also anything else associated directly with engine rotation in that specific area of the engine compartment. i.e. belt-tensioners, idler pulleys, etc.

What all have you tried yet? Have you tried removing a belt (or possibly both belts one at a time) and starting the engine? After removing a belt you can also of course check each individual pulley for slop/roughness/noises, etc.
How about using a stethoscope? Even a "homemade" one using a wooden dowel or rod may be helpful.

73Corvette

I've had great success using an old broom handle or a long necked screw driver... just start putting one end on the motor next to where you think the noise is originating from, and put your ear right on the end of the shaft... and listen carefully... if it's not that then move to another part of the motor close to that and keep doing that till you are right ON the exact spot where the sound is coming from... it's pretty damn accurate if you'll take the time, be patient and just keep searching to pin point the sound...
Please report back what you find! thanks

grantv

Is it in gear when shutting her down?

YO-EL

Next week my dealer tech & I will get into it..
Check all pulleys & tensioners..

I have the RPM billet cone (after the stock coupler was found to be cracked & an SFI flexplate), but this noise returned, so I'm hopeful its from one of the accessories!

73Corvette

Have you tried finding the source via the sound suggestions? Any luck at all?

YO-EL

Will be getting into it on the lift on Monday..
Will post up then...