Disclaimer: I'm calling the vet Monday morning. They only take emergency calls on the weekends, and this... well, is not an emergency.
This evening when I was feeding I noticed a fairly large bump/lump on the right side of my gelding's back near his wither. It's right off to the side of his back bone. It's hard and doesn't seem to bother him too much, although he did pin his ears once when I pushed on it, but they could've been because he was annoyed because he was trying to eat.
When he moves his neck certain ways it's not visible, which leads me to believe it's muscle related. But that's just my best guess.
He was out in the snow yesterday for about 1/2 an hour while I mucked stalls... maybe he slipped and strained something out there?
Any ideas? Sorry my description wasn't that great...
ETA: It's not from my saddle as I haven't ridden in about 2 weeks because of the weather. I do have a show next Saturday though... I see a scratch in my future.