Intermittent whistling / high pitched whine

I have a late (last) Nevada Anniversario 750 just over a year old from new and with 9000 miles on the clock. In the past couple of months I have heard a strange whistling noise - usually early on during a ride - that goes away if I change gear or just pull the clutch out. I thought it might be alternator bearings?? But as the performance of the bike doesn’t seem to be affected I’m leaving well alone for the time being. Does anyone have any ideas or can anyone shed light on this phenomenon?