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.