The weather today was awesome so I took the truck out for a cruise this afternoon. Just a few miles near the house. No real destination.
I was headed back to the house and I noticed a grating sound when the truck was idling at a stop light.
When I got home I found part of the problem. The rear end fluid is no longer safely contained in the rear end. It is mostly sliming up the bottom side of the bed and frame. Gear oil is everywhere. I don't know what caused the leak. And I bet it isn't pretty inside there.
I'll save that for another day.
Edit: From taking a quick peek under the truck this morning, I am guessing the rear oil seal went out. The gear oil looks like it was slung everywhere under the truck, from the muffler back. The driveshaft looks OK and the carrier bearing looks OK.