It's my belief that slop in the input shaft bearings allows the shaft to wiggle around a little bit. But I think it's caused by loose tolerances inside the transmission. It's pretty common, and seems to be benign. I think you guys are talking about the infamous 'Getrag rattle'. This is also on a fresh rebuild, less than 2k miles new clutch and TO bearing.вЂќ Mine does the same exact thing with the Getrag when in neutral without the clutch depressed, but depressed it goes away, even if it's still in neutral. вЂњДЇound on a Mitsu 3000GT forum, Getrag in a different car but still a getrag: I diagnosed this problem with one of those fiber optic cameras, and watch the TOB rattle around. This usually happens with age, as the fulcrum begins to become very slightly offround, Allowing the shift fork to not be at the right angle when the clutch isn't depressed, making it come slightly close to the pressure plate, resulting in the TOB rattling around. вЂњI used to have the birds in the tranny problem, here is how I fixed it:Д¬hanged the fulcrum and release fork, and made sure to grease them properly when I put them back on. This does not happen when it has a load on it. The input shaft has the power of the engine but the gear being spun in the cluster does not have any load so it spins up and catches the gear that spun it ,and as it bounces it resonates while spinning. When in neutral the input shaft is spinning and also spining first gear in the cluster assembly. To understand it better think of one set of gears (first gear for example) I would say when the gears are between being accelerated and decelerated that you would hear it more (at low speeds close to Idle). If you accelerate in neutral it should also be less noise - the gears dont have time to vibrate back and forth since they are being pushed to spin. 'depressing the clutch pedal should eliminate the noise - Nothing inside the trans should be turning when the clutch pedal is depressed. Д¬luster Gear end play- The trans was assembled or there is wear that it now has end-play in the cluster gear assembly rather then preload as it should have. The noise is more when there is a miss in the engine creating a vibration. вЂњGear chatter- This is when there is plenty of vibration in the transmission area the Gears that are not engaged are vibrating against their mate ,This is not a problem Most big trucks with big gears do this ,its a consequence of having huge gears to handle the capacity (BMWs with v10 always do this). The noise sounds usually like a bag of marbles rattling around inside the transmissionвЂќ вЂњOn numerous Getrag 5 speeds, they are noisy unless your clutch is depressed. Do you think switching to it after one has the noise would make it quieter? Maybe upping the idle a little somehow would help? While reading I noticed that 100% of people who say they run redline synthetic lube (75W-80 GL-4)?, donвЂ™t have the noise.

Getrag f23 transmission fluid