You did not state how old the piano was, or its condition. I had an old grand not deserving much time or money. I tried the following...First what I always try is voicing the knuckle. If that doesn't work, i glue to the knuckle what is now used under a rug before it is laid down. it is a thin sheet of very flexable rubber that I cut to size to fit over the knuckle. The knuckle is now silent. goodby Fred Weinstein
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