I have a 2007 Road King Classic. Mechanically stock except for exhaust and air cleaner. In 5th gear i have a rather loud transmission whine that goes away immediately if shifted into 4th or 6th. My dealer tells me it's normal due to the way the teeth on 5th gear are cut. I didn't know if I buy that answer. THey have suggested some ways to quiet it down such as amsoilor synthetic oil in the tranny and even suggested mobil one. THe bike performs perfectly except for the noise. Is there a mechanical fix or do I live with the noise?