I have a very similar sound coming from my driver's side door as well. Not while accelerating mind you, over sharp bumps. It's one of my only complaints with my Terrain. I thought it was the adjuster but moving it up and down or even holding it doesn't seem to stop the noise.
I'm on a Cadillac forum as well and remember someone complaining of a similar sound on a new SRX. Turns out (in his case) it was a component of the side curtain air bag system that wasn't properly insulated and so it was rattling against the roof steel.
In my case it's not bad enough for me to take to the dealer... you know what will happen there, don't you? Dollars to donuts they'll butcher and grease-smear the headliner, side panels, etc etc.