Older beat up 4 wheel drive. Rebuilt tranny and new u joints. When I get to the higher gears I have this loud knocking noise only when the engine is under load. At Idle and coasting the is no knock. 302 engine is running fine, no knock there. it sounds like a woodpecker hitting on a shovel. Everything looks sound but I can't figure out where the noise is, but it appears to be from tranny area. The knock was there before The tranny was rebuilt and I thought that was one of the problems, it also needed output bearing and a couple of gears too. That slave cylinder was nasty to bleed, anyway, any direction of where to go and where to look would be great. I miss the simple days.