We have had some bobbling hammers on almost brand new Yamaha U5s (and some older ones, too) here at University of Nevada, Reno. Check your key dip. A couple of appropriately placed business cards under the balance rail might fix things up real fast. Seems the key beds start to sag just enough to give trouble soon as the piano drys out. Try it, you'll like it. Ray Diederichsen University of Nevada, Reno
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