If the clutch has been replaced by a competition item, with different rate central damping springs, or no springs at all and the flywheel is a solid flywheel, then the damping between the crankshaft and gearbox gears meshing is 'not as factory' (or non existent) and on deceleration, some resonant backlash noise will be heard (probably around 3000rpm on lift off)
If the noise disappears, when the accelerator is lightly applied, then it's perfectly normal.
Using a slightly heavier 75W 90 grade gearbox oil than the factory 75W 85 can quieten the noise, but adds a little mechanical drag.
Hopefully this helps;