SOLUTION FOUND!!!

I was fighting with this for years. And I was just contacted by a member to see if I found a solution, so I thought I would update this thread.

I ended up using black butyl tape (kind of mastic on a roll you get at Home Depot.
Between the roof and the deflector. My deflector does not sit flat (flush) to the roof on the outside corners. So that filled in the gaps nicely.
(If it needs to be removed, you have to use nylon fishing line to cut it off. And it leaves a mess that you need plenty of mineral spirits to dissolve. )

But the problem did not go away!

Because the damn problem was something completely different than I thought it was.
It was NOT the sunroof.
It was the A-pillar black plastic windshield molding (bezel) on the passenger side.
That is designed to be removed when replacing the windshield.
The top of it was rattling. The top of it is loose by design. Bad design.
I put a tiny bit of black urethane caulking (Again from Home Depot) into the space between the top windshield rubber molding and the top of the black plastic bezel
Just to keep it from moving and vibrating at higher speed. Problem solved.

Test the theory. Tape it down and drive your vehicle at highway speed.
It is possible that your RIGHT side is also vibrating. Or both. Depending which side of the vehicle the noise is coming from.

Such a simple and quick fix, but took years to figure out what was wrong.

Post here if this solves your problem.

 

I bought my 06 H2 in March and have been chasing down that same high speed rattle to no avail until I found this thread.
I have only managed a temporary fix but will get that urethane caulk applied asap.

Thanks for updating your thread and relieving my frustration.

 

https://www.hummerforums.com/forum/h...driving-37804/