Hi Carol,

It could be a calcaneal spur. Alot of people have them and never know about it is found incidentally on an Xray.However they can get painful from time to time especially after alot of weightbearing exercise.
Basically it is an overgrowth of bone on the underside of the calcaneum (os calcis) Nobody really knows why they occur but I have found a large incidence of them in people with high bone density in my work with osteoporosis.
You haven't been overdoing the calcium or been on a calc remedy have you ??