Deep callous on back from squats.

Hello,

I am 50 yrs old, and have been squatting on and off, for circa 25 years,
with a standard olympic bar. I use 315 - 345 lbs for 1 or 2 sets of 10
reps. I have noticed a raised callous on my back, that my Wife, and
chiropractor notice quite prominently. My questions are:

1. Is this normal?
2. Will a bar pad help?
3. Can musclature in the affected area reduce/eliminate this callous?

I was doing hack squats, in place of squats. After about a month,
though, I found myself missing the "joys of squatting" and have started
squatting again. Any information, and/or comments would be appreciated.

Fatman Squatting, medics!! Fatman Squatting,

John