On Tuesday, November 12, 2013 5:05:23 PM UTC-5, James wrote:

Does it have bladed spokes?

I wonder if they are somehow vibrating with the air passing over them
after a bump sets off the oscillations?

It might be that the spokes just need to be tightened to increase the
resonant frequency?

Or, as a temporary test, fasten a bit of extra mass to the middle of each spoke, to lower the resonant frequency? See if it happens at a different speed? I suppose a bit of solder taped in place on each spoke might suffice.

Some might say a "tie and solder" job would be in order. But if those are radial spokes, it would be tricky!

- Frank Krygowski