Tinel's sign is an electric sensation that results from tapping on a nerve that is aggravated or compressed. Check simple mechanical causes. The calcaneal nerve is very superficial and not well protected depending on how much fat is in the area. If you are bony and wearing shoes with a tight heel cradle (like a lot of athletic shoes have) then it just might be getting smooshed when you walk. Make sure you have enough room and consider cushioning the area.