2010 HARLEY-DAVIDSON FLSTC Wheels Problems

I WAS DRIVING DOWN A HILL AND I LET UP ON THE ACCELERATOR. THE BIKE BEGAN TO MOVE SIDE TO SIDE UNDER ME. WHEN I BEGAN TO ACCELERATE IT SMOOTHED OUT. I TOOK THE BIKE TO MY LOCAL HARLEY MECHANIC. HE LIFTED IT UP TO FIND THE REAR SPOKES COMPLETELY LOOSE. HE TIGHTENED THEM UP AND IT WAS FINE FOR A WHILE BUT I CONTINUED TO PERIODICALLY CHECK AND TIGHTEN THE SPOKES. A FRIEND HAD A 2005 FLSTC WITH 45000 MILES HE PURCHASED NEW AND NEVER HAD TO TIGHTEN THE SPOKES. MY MECHANIC HAS BEEN A HARLEY MECHANIC FOR 30 YEARS AND USED TO OWN HIS OWN DEALERSHIP. HE SAID THERE IS NO WAY THE SHOULD HAVE COME THAT LOOSE IN THAT FEW MILES. *TR