that "clicking" noise only in 4hi?

[aznpersuasion]

i searched and googled for clicking noise on decel, slow down, 4hi. i looks like a lot of the problems stem from loose u joints or worn bearings however that sounds like it would be a constant sound. i only get the clicking in decel in 4hi. now after i put it in 2hi like it should be noise goes away. in 4hi on acceleration no noise. i think the previous owner may have run the truck in 4hi constantly here in socal and could that have damaged the driveline?