Odd sound and clunking

I have an '01 Chevy Tahoe 4x4. For a while now, when I let off the gas it makes an odd sound but it was faint almost like tires on the road so never paid much attention. Now the noise has gotten really bad almost sounds like metal rubbing, but it only happens when the the truck is decelerating. The moment my foot releases the gas it begins. Earlier I was dropping from about 70mph to turn and the truck shook back and forth and felt as if the bottom was going to fall out. I made it to my destination parked for a few minutes then left again, the noise continued but when I pulled in the park and coasted for a moment there was a loud clunk and the truck stopped. I put it in park got out and looked under, I didn't see anything unordinary. And it drove to a parking space just fine, aside from the grinding noise. What could this be?