Avery....we have 2 american steinway Ds and one of them does this when we move it from our humidified hall to the big "dry as the sahara desert hall"....so i have to make sure to re-bed the keyboard after the instrument has gone through the change....and yes.... you must shim at the top of the glide plate (this is the proceedure taught in the steinway factory school).... just loosen the four screws and wedge the glideplate down w/ some veneer... so you still have a metal/metal contact if you have a really drastic difference maybe you'd need to redrill....anyway they teach the shimming at the factory school....i believe its in the manual published by Steinway....but,if you have the chance sign up and go...its worth every second you're there....and scott is a great teacher.... Rich Adkins Coe College
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