2002 Buick LeSabre making a loud sound when driving it. It gets louder the fast I go.

It sounds like the boot on your CV shaft has split open and you lost all of your grease. Look on the backside of your front wheels. There should be a shaft with a rubber boot at either end. Check those boots for a large split. You should see a lot of grease on the bottom of your car if it has split open. If no visible split, it may not be the CV joint. You may also have a bad wheel bearing that has dried out. I would suspect that one of the two is your culprit.

Did your muffler fall off?

Jamnblues could be right on the money. Start your car, then get out and put your hand flat right over the end of your exhaust. Press your hand really hard against the end. If you hear a loud hissing noise coming from underneath, then you have a broken exhaust pipe, muffler, or manifold. If you hear no hissing and your exhaust builds up pressure to want to blow your hand off the end, then your exhaust if good.

The muffler did not fall off. This happened over night. Someone else said it may be a catalytic converter and that it could have been stolen. Is there any place I could take it that could trouble shoot it without costing me a bundle?

Well hopefully nobody stole your cat converter. Then it will cost you a bundle. Take it any place but the dealer...they are the most expensive.

Did you find out what was the problem. My Buick seems to be having the same noise.