Buzzing noise from rear Mavic hub?

[Pierre]

Morning, crew. I've got the oddest noise coming from the rear end of my bike.

I ride with Morning Glory out of Toronto (west end chapter) and the weekday morning circuit takes us down a very short and steep hill followed an abrupt left hand bend with a continued downhill.

My bike is absolutely silent until I get to the apex of the downhill left hand turn where I'm going about 50km and leaning in pretty hard to make the turn. Three times now, at that very moment, I get a buzzing noise that seems to come from the rear hub. At 50km and turning, it's hard to take a time-out and look downwards and back to get a real sense of where the noise is coming from...The buzzing continues for a bit (say 100m) and then ceases.

The wheel spins straight and there is no roughness to the bearings that I see detect.

The sounds takes place regardless of whether I'm pedaling or not...

Any thoughts?