Hi all. I just got off the phone with Yamaha customer service. Aside from being very helpful, they did confirm that this is a known problem although the person couldn't offer any details as to what happened to cause it. The good news is that a service bulletin is on the way to the dealers. The issue is so new that it hadn't gone out yet. Interestingly enough, the TSB is not just about retorqueing the nut to a new value. She also mentioned that there is a new "procedure" that goes along with it. She couldn't offer any details. If your dealer doesn't know about it, have them call Yamaha Tech Support for the TSB, or wait till they get it - it should be coming soon... I hope.