A month or so ago I was driving my truck and took a turn from blacktop onto a dirt road. As I went onto the dirt road I heard a noise start up from my rear end - sounds like a stick or piece of wire or something got caught up underneath the vehicle, like in a wheel well or something, and was sort of whapping around on things. I didn't think anything of it, figured I'd just ran over a stick or something, and picked up a load of rocks. I drove from there up the street about 30 seconds or a minute away, still hearing the noise, and dropped my rock off. The next day I got in the truck to go to work, and as I reversed I heard the noise again, so I got out to remove whatever was under there, but couldn't find anything. So, I hopped into the wife's car, ran my errands, and then left out of town for a month of work. I got back yesterday, and today started trying to figure out what the hell is making that noise. I tried jacking up the rear end and spinning the tires - no noise except some gentle drum against shoe friction. I thought one wheel felt a little different then the other, so I pulled the wheel, axle and hub, and everything looked fine - the bearing looked normal, gear oil looked normal, no crumbling brake pad or anything like that. Put it back together and tried giving it gas in forward and reverse with the rear end off the ground - no noise at all. Dropped it back down and as soon as I try to go anywhere, the noise is back.
It's definitely coming from the rear end somewhere - I looked for cracked springs and couldn't find any. Tried jumping up and down on the bumper and it doesn't make the same noise - just a little creaking. Tried wiggling the driveshaft, and I have zero play in it.
The noise sounds kind of tinny and metalic - not perfectly repetitive - maybe like loose metal in the differential??? I don't really want to pull the dif cover, lose all my gear oil, and have to reseal everything if that's not where the problem is - has anyone heard noise like this before? I'm thinking it's the dif - certainly doesn't seem to be the passenger wheel - haven't pulled the driver yet, but I would have thought I could feel it when spinning by hand if that was the problem? Driveshaft maybe? Any help would be much appreciated - it's weird - there's not that much stuff back there so I thought that whatever the problem is would be super obvious, but it doesn't appear to be. Thanks in advance,
PS haven't had anybody around to help listen where it's coming from yet - will do that later today when the neighbors get home.