<div>List -</div> <div> </div> <div>Due to the many and varied ideas tossed out there I was able to solve this puzzler, and while the answer - as always - is something quite simple, I have never run across this in almost 3 decades.</div> <div>  </div> <div>Exchanging wippens left the same hammers with the same problems, so the wippens could be ruled out as part of the problem.  Interestingly, Ed Sutton's suggestion of increasing the height of the rest cushion actually seemed to cure the problem for 2 of the 3 offending notes, but 2 outta 3 ain't batting 1,000.  Some new evidence I discovered tonite was that you could create the problem on the very first strike if it was swift enough.  You could also play a soft trill successfully forever and then sneak up on it with a very swift forte blow and cause the backcheck to snare the hammer on its way up.</div> <div> </div> <div>The problem turned out to be 3 knuckles that, although brand new and factory installed on new shanks (from Wally), were actually fairly misshapen, particularly being VERY concave in the center of the knuckle on the side the jack travels (towards the player).  (Oddly, the non-business side of the knuckle was perfectly shaped.)  Anyway, this necessitated moving the jack a tad further back than usual so that on a swift blow it wouldn't just kick out of the way before pushing the hammer very far upwards, allowing the backcheck to capture the languishing hammer.  There was never a problem on softer blows, no matter the speed of repetition.  Weird...  </div> <div> </div> <div>A new one on me, and one that I will be on the lookout for in the future.  Hopefully this will save someone a little head-scratching someday.  New knuckles apparently aren't exempt from causing mysterious problems.</div> <div> </div> <div>Muchas gracias to all!</div> <div> </div> <div>Mark Potter  </div> <div> </div> <div>  </div>