Thanks, I didn't spray anything, just blew the dust out of them. I'm still getting the belt chirp, in high gear only, not all the time but it's never done it before last weekend. Think I'll look into a new belt, there's 3000km on this one.
I also changed the oil in the rear diff, it didn't look bad but probably didn't hurt it to change it. No water or metal in it, just the normal flecks I'd expect. While doing this, I may have found something that has a non-zero chance of being the source of my coasting on rough hills clunk.... My damned trailer hitch! It's loose enough that it kinda bounces around, similar sound but I can't be sure until I've driven some regular trails with it removed. I'm not confident this is it but I will see.