Bobbling hammers. Chinese, Korean and Japanese as well as German pianos ARE of different design! They have individual hammer return springs etc. While they OCCASIONALLY may "dance" they also repeat faster. The problem with many of them is that if not regulated properly the "dancing" becomes excessive. If the problem goes away when the sustain pedal is depressed AND if it only happens with some keys(!) the problem can be minimized by weakening the damper lever spring. Ernie Juhn
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