1980 Pontiac Trans Am

Noises problem
1980 Pontiac Trans Am V8 Two Wheel Drive Automatic 80000 miles

i own a 1980 pontiac trans am with a chevy 350 5.7 ltr. V8 engine and a TH 350 transmission in it. All parts are brand new and have about 3000 miles on them in the 4 months ive owned the car. My question is whenever I let off the gas to begin a coast beginning at 25mph a grinding / rubbing noise occurs and gets progressivly louder the faster I coast. But whenever I decide to give it even the slightest bit of gas during the coast the noises stop. However getting up to 55mph I get very bad vibrations on the drivers side. This all started occurring a week ago with no changes made to the parts in the car or the car itself. Any ideas? Im stumped.
August 22, 2010.

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