I have to agree that it is almost certainly a spun bearing. Some of these engines in the 6g7X family have what seems to be a higher than average incidence of spun bearings. The sound and symptoms are exactly what a number of people who have spun bearings on their 3000GTs and Stealth have described. Don'r run the car any further-the motor will seize up.

I would recomend you join up on
3si.org
3sgto.org
6g72rwd.forumcircle.com
and let people know your story if you want to try to save your Monte. It is possible, although far from certain, that someone may be near you and able to help you in your situation.

Best of luck!