Squeaky Stairs

This house is 28 years old, and the interior stairs squeak. (Use wood glue and screws instead of nails!) For the past 9 years, I've been trying to figure out the pattern ("step here, then there") to squeak the least. But in the past few months, I discovered that I've been following the wrong approach. This isn't a position-dependent problem, but time-dependent! The faster I go (within reason: falling down the stairs at night would be very loud too), the less squeaking. The only exception is the third step from the top: it always squeaks.