Drivetrain Problem

2003 Mustang GT 5sp

The problem with my car is when I’m cruising
in any gear and take my foot off the gas while
the car is in gear it while make a rattling/grinding/
scraping sound. If I give it gas it goes away or if I push the clutch in it goes away. The noise sounds like it’s in the rear one day and in the transmission next. I took it to the ford dealer and they claim it
was a problem with the rear, I had the rear rebuilt and the noise is still there. Any advice would be greatly appreciated. Thanks