Rear diff issues

[Chrispbrown36]

After fixing an ignition issue on Friday I decided Saturday night would be a great night to do some jug fishing. Hooked up the boat and made the hour drive to a new spot. As I got off the interstate turning on to the highway I hear a clunk. Pulled over and looked things over. Nothing really stood out....the u-joints feel tight....but forward and reverse at low speeds I get a clunk with every wheel turn. After I got it home I took off the rear diff cover to look things over. The lube seemed to have been a little low, but nothing excessive. There was a little bit of metal shavings on the magnet, but no big junks. I jacked up both sides and moved things around. The only thing that seemed odd was the driver side seemed to have more play in it than the passenger side. Wiggling it back and forth and pulling it in and out. Any ideas?
And for those that care....the fishing wasn't great. One little channel cat just before I left.....but man was it gorgeous out there last night.....almost nice enough to make me forget about my truck issues!