Loud Noise when car decellerates while i n first and second gears

[some mech 3]

This is a follow-up to a Dec 12 post titled Transmission Assembly. To identify the metal-banging noise I have rebuilt the transmission and put in a new U-Joint, clutch, and pressure plate. These did not remove the noise. The noise is a continuous banging until I push down the clutch pedal. In ordinary driving the car runs beautifully. I welcome your insights. Thank you.
Some mech 3.