Hi All. I have a daily driver 89 22re regular cab 4x4 manual trans and the other day it starting making a loud "clacking" noise only while the truck is in reverse. It doesn't happen in any forward gears. It is also louder when there is more load on the drive train - ie reversing up a hill or with a load in the bed. Also the frequency of the clack changes proportionally with the speed of the truck and it occurs all of the transfer case gears - 2h,4h,4L.

I inspected the the drivetrain with the rear wheels off the ground while idling in reverse gear and it sounds like its coming from the transmission. All of my U-joints are decent and its not the front IFS components.

Any ideas? thanks.