so my 929 with 20k miles when i picked it up from my dad made an obvious vibration noise from under the tank at about 3600 rpm to 4k rpm. last week i noticed that noise and vibration is gone! i was told the original noise/vibration was normal and it was the flapper. but why would it go away? bike seems to run fine with no flat spots (i checked that on a nice safe back road this week.) any input guys/gals? thanks so very much!