My boyfriends truck (ford ranger.. 94 I think) has started to make this weird noise. It comes from the back of the truck and its like a clanking sound, but it sounds kind of like back in the day when you clip a baseball card to your bike tire. It doesn't do it all the time, so he doesn't think it's the axel, but the other day when he was breaking it sounded like metal on metal, so he thinks his rear breaks are worn out (he hasn't replaced them in 17k miles. Does this sound like a possible solution, and if so, how easy is it to fix yourself?

Sounds like it could be a ball bearing possibly.
If he takes it to a mechanic and they take the tire off they should be able to tell right away if they can't tell by the sound.

. Look under the truck and see if any road debris (e.g. plastic bag) has wrapped around the driveshaft.

. Pull rear drums and do a visual. Many brake outfits will check brakes for free.

. Check differential fluid level and driveshaft universal joints. If you hear a clunk noise, when the transmission is dropped into gear, then the universal joints are possibly bad.

Metal-on-metal sound leads me to suspect rear shoes are shot. My advice is to stick with OEM brake pads and shoes.