crazy tc noise

so my buddy has got a 99 cherokee with 200k with a 40 aw4 np231 and d30 d35. so he gets this crazy noise above 50 mph coming from the case so we put it up on a lift and listened to it and it sounded like it was the support bearing from the output shaft on the tcase and the noise was echoed through the drive shaft. so he had another tcase laying around and we installed that one and the noise is still there and its in the same place. so we pulled the driveshaft out and ran it and there is no noise. so we started investigating the pinion bearing but it didn't feel gritty or anything. it felt pretty good. we put in a different drive shaft from another jeep and the noise was back. nothing has excessive play and the jeep sits bone stock. the only thing i can think of is when the trans goes into overdrive somehow its putting pressure on the input shaft of the tcase which is putting pressure in the main shaft in the tcase possibly forcing the chain to rub or cause a bearing to have lateral load and echo through the extention housing. but if so then how come it dosent make a noise when u pull the drive shaft. i know there is some load taken off but is it enough load free spinning in the air to cause a noise like that? any input would be great thanks.

Wow that was kinda hard to read. So you just swapped the extension housing out and not the entire xfer case?