This seems to me to be of serious concern to all 4600 series owners and potential buyers. The sound is not well enough defined for anyone to figure out for sure what you are talking about. For sure you need to get to the bottom of it before the warrantee runs out. There are a few questions/answers that might help narrow it down:
-- You said high gears or under load. You are not talking when it is lugged down severely are you ?
-- Chatter is the only descriptive term. Not much to go on. Do you have a way to record a You Tube video that we can watch and listen to the sound ?
-- Is this all the time or under exactly what conditions ?
-- Does it matter what level of raise/lower your 3pt hitch is in ? Only when lever is fully up maybe ?
-- Can you find any other control or circumstance that it must be in in order to produce the noise ?
-- Does it matter if the 4WD is engaged or not ?
Good luck.