Hi Tricia,
That's why I've posted in this forum, I don't want to go to the dealer and pay them $150 just to find the rattle (not yet at least.lol) if it's something common and easy to fix that someone else has experienced and done.
Unless GM dealers treat Cadillac owners differently I expect to get charged a full diagnostic fee + what it'll take to fix it, they even charged me to do a diagnosis for my shaking engine on my 95 Suburban (Brand new GM Goodwrench 350 motor) that was installed at a GM dealership and to this day is still under warranty. First time they said the motor mounts were not replaced when the engine was installed and that they were now bad. After we replaced them ourselves, the shake remained. This time we took it to the dealership that did the installation. They charged us a diagnostic fee and said nothing was wrong and we should just drive it till it dies. In my opinion, if you spend $4500+ on a brand new GM engine and GM dealership installation, the engine should run smooth and shouldn't have people asking if something is wrong with the vehicle.
If the engine were old I could easily live with the shaking, but we're talking about a brand new GM engine here, and it shakes like there's no tomorrow. The dealership official response to our problem is that, "that's just how those engines are".
Back to the Cadillac
If this Cadillac was new and still under warranty I'd go to a dealership right now, but it's not.
Normally I wouldn't post the vin, but I'll take a shot in the dark. It's 1G6DP567950185710
Whether or not you can help, thanks for your time. If anything it's let me vent my frustration about GM customer service.