Hey crew! It's been a while.

Just had the gearbox (FSSR30A) rebuilt on the old RB30, after 400k the synchros on 2nd and 3rd were getting a bit crunchy. Full bearing kit, synchros plus a a few hard parts (4th/input and countershafts, 5th, reverse). Did the clutch as well.

Unfortunately something seems to have been missed or the box has been installed wrong, and the things are sounding more concerning than ever did before...Hopefully you can see this video (google drive link - https://drive.google.com/file/d/11Q1...ew?usp=sharing). Video is coasting from 40km/hr to a stop with the clutch in (pedal to floor) the whole time, shifting between the gears and neutral.

A few diagnostic details - the noise only happens with the clutch in (i.e., pedal to floor). It's a cyclic 'chatter' sound that turns into a shudder that shakes the vehicle at low speed, like the handbrake's been left on and dragging. Noise corresponds to the speed of the vehicle (noise gets slower as speed gets slower). Noise is the same in all gears and in neutral (i.e., doesn't matter where the gear shifter is, only that the clutch is in). When driving along as normal (i.e., gearbox/clutch engaged) the sound isn't there.

Has anyone heard this sort of thing before, of have any ideas what could be the matter?
Cheers fellas