Crusty clump under her chin?

I've been keeping an extra close eye on my chinchilla lately because she seemed to be acting a bit odd. She's been sitting in unusual places in her cage, and doesn't seem to be eating much hay or pellets (but sure does spread it around). She does get very excited at the prospect of a treat though, she seems to be pooping fine, and I hear her running in her wheel in the night after I've gone to bed.

A couple of times in the past I've noticed that she had some crusty junk in her fur under her chin. I was worried about tooth problems each time, but they were individual incidents that were spaced out so I figured she just got something in her fur (like maybe juice from a piece of fruit).

Yesterday she had a bit of it in her fur under her chin again but I didn't think much of it because she had a bit of something stuck in the fur on her back a few days ago... but today it's worse and she's got a clump there now. I tried to crumble it with my fingers but couldn't and she was clearly miserable about it so I thought I'd leave it alone for now.

What is going on? I'll be calling the vet tomorrow to make an appointment, but I'm pretty worried about the little bug now so I thought I'd see if anyone knows what this is...