There are a number of sources of such noises and may take a little time to check them all out. Glazed knuckles, use a suede brush to brush off the glaze and raise the nap. Rocker cushion can be hard, brush also but may have to be replace eventually Backrail cloth, vacuum, brush and consider it's quality, thickness, for replacement Balance hole for loose fit around hole, shrink with water or steam Hammer "rest" felt may be overly hard Hammer shanks too close to rest cushion Damper levers could to too close to key end felt, time the damper Hammers could be hitting backchecks, evaluate and consider lowering backchecks Loose action screws, screw them up (tight). Wippen support post pin loose, repin for some but minimum friction Jack return cushion is too hard, squeeze with needle nose pliers and regulate Keyframe may need thorough bedding Dampers could be overly hard and thumping upon return. Other parts may need tightening, easing, adjustment or aligning. That should keep you busy for a few minutes. The best diagnostic technique is to isolate each individual source of noise and check them one at a time. Also consider that more than one is contributing to the problem. Have a nice day all. Newton
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