The clutch plates will often dry out on the RFS'. With just over 1 quart of oil in the motor and not much directed at the clutch plates it is not unusual to hear a "howl" as the plates slip against one another. It tends to get worse while doing a holeshot. An easy fix would be to drill the inner hub to allow oil to get to the clutch plates. Back in 1987 KTM had a problem with their 250,350 and 500's and issued a tech bulletin to fix this type of problem.
------------------