My 99 D is making a "rattling" noise when comeing to a stop, It only happens when you let up on the gas at at really any speed but can really hear it good when comeing to a stop. It really sounds like marbles in the cat is moving around. Only happens when letting up on the gas? Not when giving it gas.
I got under the D and pounding on the muffler and the cat to see if I can hear any rattling and theres nothing? I dont see any damage to anything. I cant see or feel any loose metal under there either?
Any help?

Check for cracked or broken heat shields and broken exhaust hanger. Tail pipe might be hitting shock or something.

Thanks Todd, I try and let you know.

FYI, i finally figured it out,
It was the front right brake backing plate! WTF!
it was too close to the rotor and would rattle just enought to aggrevate!
Bent it back and all is good!

thanks

Thanks for posting back. Hopefully this will help others with their problems. I'm gad you found your problem.