Bump on base of salamander tail?

[CritterChitters]

I found a bump on the base of my tiger(.?) salamanders tail. i dont know when it popped up, but it wasnt there last time i looked him over a couple weeks ago. its raised and kind of rough, bu its small, i think it may be a scab, but im not sure from what?

i got him from someone who caught him in their garage, so i dont really know anything about his past and hes from the wild, but ive had him for a couple months now and this is new.