I am not sure how the Getrag box is for gear chatter, The T56 or almost any of the late model Tremec gearboxs suffer from chatter at idle, but it is a problem that alot of gearboxs suffer from and is not nessicarily a big drama. If it were a bearing problem it would be present all the time through the rev range. Alot of late model gearboxs run a spring loaded sling on the drop gear of the lay shaft, sometimes this can fail and the result is gear chatter at idle, which is annoying, but not lethal.