Driveshaft clinking noise

I have a 97 Blazer 4 wheel drive with over 100,000 miles. Every time I put it in reverse I hear a loud clinking noise.
Can anyone help?
Thanks

is that the only time you hear the noise/clunk? could just be a bad u-joint.

Or the rear diff has play in it as many GMs do. Also check the diff 80w-90 gear oil, 2 plugs so remove top one and should feel it with finger full. If never changed good time to do it. Same with front diff, xfer case, and hope the trans was done too!

Are your emergency brakes in good order? I dont know if the 97 has the same set-up as a 98, but mine were shot and were rattling off the rotors, it was always more noticable when backing-up though. Might be worth checkin into if all else leads to a dead end.