Sounds like the sub floor or the actual hardwood flooring was not fastened properly in that area. Sounds like the sub or hardwood flooring is dancing up and down on a finish nail not properly seated.
This could be a night mare to fix. Does this happen during all seasons or just recently since your using your home heater? Did it do this during the summer with cooled air?
If your haveing company for Christmas Day or any special occasion where this squeak is embarrasing you, the night before place a bag of ice over the spots and let it stay for three or four hours. The moisture and the chill will contract the wood to the nail and stop the squeak. THIS IS ONLY A BAND AID.
You will have a better chance of fixing this if your on a peir and beam foundation. Go under and carefully screw or shim the squeaky area. This is a two person job one with a set of two way radios to communicate. One to be under the home the other to walk around locating squeaks.