Tapping sound when I let off gas

What is your question?

Recently got 3.55 performance gears installed, 31 spline trac lok differential and 31 spline moser axles..

What makes this problem better or worse?

Better when I press the pedal and worse when I just let off the gas going 30+ mph

How long has your 2003 Ford Mustang had this problem?

1 week after I got them installed at a mechanic shop