Rattling noise under the rear end of 2001 mercury cougar. Feels like car hits bumps hard. Suspension time

Did you change to a different type of tire or tire size that is called for on the car is specifications. A lot of the newer pneumatic tires using an oversized rim can cause that. Or if you flip your leaf springs to put slicks on the back. (an old trick of the 70's).

You might address the problem to your nearest mercury dealer.

probably a loose tailpipe, take it to a shop and have them put it on a lift and check it out..

HAVE SOMEONE CHECK THE EXHAUST SYSTEM AND THE REAR SHOCKS.