Thanks to all for their helpful replies. I was already considering most of the various diagnoses, except for Richard's warning about checking the bridge notching. As it turns out the customer called the NYC dealer about it after I was there, and this time the dealer fumed that *no one* other than their own designees are authorized to even diagnose (let alone fix) the problem! Hopefully this means that they're going to do something about it; meanwhile it's not my headache anymore! Patrick Draine
This PTG archive page provided courtesy of Moy Piano Service, LLC