Have you listened to someone else's drive out of the water ? If not, will be a good idea for a reference.

Easy..Started the other engine..no noise from the drive at all

Sorry you had to witness my brief battle of sometimers.

No Prob. I had a noise at (sometime) on the other NOW quiet drive..It wasn't as pronounced as this but sounded like a rattle coming from the upper. I never did anything about it and it seemed to go away. The merc mechanic at that time said it was a resonating sound from the engines cam and the sound being under the back of the boat...Of course i never agreed but its been fine since....

Bummer, thought for sure you had it this time out

Is the Coupler greased heavily,, if dry or very light grease they will rattle

Ok, They took the drive apart today and checked the preload on the input shaft bearings..It was holding at 5.5 inch lbs. They took it all apart again and checked the bearings and then re set the pre-load for 7.. Looking further hey did find the drive shaft bad. It is the shaft that sits in the center of the top and bottom gear along with the cone clutch. That shaft doesn't spin in neutral but the top and bottom gear do with the bearings that sit on the driveshaft. Hopefully that was the noise i heard...There goes another $400

Hope they remember to set the timing marks correctly

I even know how to do that now...lol

I would say if the rattle was coming from the coupler my spline on the input shaft would be bad and /or the coupler spline and the noise would be inside the boat. I was told that when you grease the coupler it is only for the spline so it moves freely when trimming, turning etc
I always put a lot of blue merc grease on the spline when re-installing my drives