Going nuts! Strange clicking in front hub

[AirSpeed]

I've had a strange clicking noise coming out of the left front hub on my 72 GMC 4X4, it only happens in reverse. I jacked it up and spun the tire in both directions and can't get it to make the sound, it has to be on the ground and backing up. I replaced the wheel bearings but that made no difference. I installed new locks and no help. The u joints in the axle are fine and it makes no difference if it's in two or four wheel drive.
It's driving me nuts! I'm also in search of new bushings for my leaf springs, bought some rubber ones from LMC last year and they're already destroyed, chunks are hanging out. Where do I get good bushings?
This noise has been bugging me for a long time! Any ideas?