I have 1000 miles on my brand new (March 2020) Burgman 400. It was smooth as glass. Rear tire damaged, managed to keep enough air in it to get to the dealer, who replaced the rear tire. Since then, when cold, and occasionally when warm, at zero to 15 miles per hour the transmission pulses rapidly, seems to slip a little then catch, in fast rhythmic pulses, in about the rhythm of someone knocking on a door. Did the tech at the dealer maybe not get the belt tight enough when he reinstalled the rear wheel? Something different!