Noisy Gearbox

Hi all,
I have a knocking sound coming from the gearbox. when I press the clutch pedal, it disappear and when I release it, comes again.
Last time I renewed all gearbox bearings and the problem still present.
I removed the gearbox again. I turn the input shaft with my hand to feel if their is grinding noise or anything suspect, to my surprise its good.
I re-assemble the gearbox on the engine, start the engine and the knocking sound still present.
The engine is in good conditions already being revised.
... A friend told me to verify the clutch disc, plate and the release bearing.
Anybody can clarify me on this matter.
Thanks

yes I once had a loose rattling clutch plate spring.

when it was in neutral (no load through the clutch)
with clutch engaged (disc spinning)
and idled below 800rpm (not enough centrifugal force on the loose springs)
the loose clutch springs would just rattle about in their housing due to gravity.

can be resolved by either increasing the idle speed, slightly hammer the clutch plate spring retainers abit tighter to reduce the slack, or replace the clutch plate

Thanks asdame. I`m also thinking about that. Hope this will solve the problem. thanks bro.

;)