Cool, hopefully it was just dirt or a rock
As for the u-joint...
It's easiest to see on the rear of your vehicle, look underneath and you'll see where the drive shaft and the differential/transmission, depending on which end you're looking at, come together are u shaped. In between there is a + shaped joint that holds them together, that's the u-joint. On the front there are the factory skid plates in the way so they're a bit harder to see.
If you can get to them, check all the little rubber seals where the joint connects to the drive-line and differential and transmission. Be sure to check all 4 points on all 4 of the joints, I thought my squeak was coming from the front but had someone get out and listen and it turned out to be the rear. When they're going bad you can see the rubber coming apart and chunking/flaking off.
You can't grease them, I ended up replacing mine with an OEM one cause he said it would be a couple days wait to get one with a Zerk fitting so I just had him replace it with what he had. Cost me $50 for the part and $130 for labor, not sure why it took so long, not really a hard fix. You could do it yourself depending on how confident you're feeling
I'd recommend getting a stronger, beefier, one with a Zerk fitting if you need to replace it...I just wanted/needed my truck back so I figured I'll just replace it again when it goes out.
here's a pic, not our truck, but you'll get the idea