'71 K20 Growling/Grinding noise

[flyingtim01]

Hey Guys,

Saturday morning I got into the truck to go pick up a new dishwasher. Halfway there, before I even got on the highway, I started to feel this growling/grinding noise from under the truck as soon as I hit 35-40 mph. Got on the highway, and it feels like it mostly went away around 60-65. Got back off the highway, and slowed to 35-40, and it came back. Loaded the truck (after it sat for about 30 minutes) and it didn't immediately come back. Did 40 mph or so for a while and it was quiet, then I hit a bump and it came back. Got back home and parked it and got to work on the dishwasher.

Sunday morning, I went and picked up a cord of wood with it. As soon as I got onto a main road, the growling came back. Loaded it with a full cord of wood, and got it back out onto the main road, and the noise was gone, or at least severely diminished. (No insulation/carpeting left in the cab, it's pretty loud even when it's quiet)

Just to run down the list of obvious things: U joints are all greased (all of them), axles have plenty of oil, as do the tranny (SM465) and transfer case (NP205). It doesn't feel like a vibration from a tire. After I parked the truck on Saturday, I went around feeling the hubs. The only one that was warmer than I thought normal was the right rear (full floating eaton) so I'll have to take a look at that. Isn't that bearing oiled directly down the tube from the pumpkin?

Anyway, the grinding/growling seemed to be coming much more from under my feet, so I was thinking a front wheel bearing, though nothing was hot in the front, and I've never known a bad wheel bearing to get better the faster you went.

It is odd that the noise almost completely went away when fully loaded with a cord of wood though, so this afternoon I'm going to crawl underneath and see if anything is contacting the driveshaft or something along those lines. I wonder what would be different when the suspension flexes (it seemed like going over a bump triggered it to start with, and then when loaded down it goes away) so I guess I'll have to eyeball everything. Any suggestions?