<html> <body> Theory. I agree that it is highly improbable that the string climbs up the pin. However the pin can rise out of the bridge, due to hydraulics. As moisture is absorbed by the bridge, force is applied to the bottom of the pin, moving it upward.  This is the same principal as rocks appearing in a farmers field every spring.  Movement of water , pumps these rocks to the surface.   The string is held against the pin with friction, and rises with the pin. For a number of years I have been using West systems epoxy as a driving fluid for installation of bridge pins.  The pin acts as a pump and forces the epoxy down the capillaries of the grain structure, making the hole/pin impervious to these moisture fluctuations.  The number of false beats to appear in bridges with this treatment is way less than no treatment.  Many of us have repaired bridges with epoxy, putting the epoxy in hole #1 and watching come out #2. If the pin has moved upwards, then this can explain why a light tap will seat the pin and string, and be a partial cure for several years.  The hydraulics with begin to do it's evil work again.   New pianos going to a very dry climate will exhibit shrinkage of the bridge, and can show a lot of falseness. Seating the strings by tapping the bridge pins cleans up a lot of the garbage, and lasts for a number of years. I have had several long conversations with a Professor that specializes in soil Hydraulics, and does a lot of consultant work for major power corporation's , with regards to transmission lines.   The telegraph poles that you see beside the highway, leaning every way but vertical. Are moved by the following. #1 Hydraulics. #2 wind shear. #3 load. He felt that my theory was a high probability. Regards Roger. PS I will keep tapping the falsies out.</body> </html>