[ShrimpBurrito]

I don't know about the axle, but the "phenomenon" you describe is typically the result of either unbalanced tires (do your rims have lead weights attached?) or tire pressure that exceeds about 70 psi. The latter would only be the cause if you either you overinflated them, or you have tires with a high load range that requires a high pressure to support the rated load.

My guess is your tires are not balanced. Since that's a cheap and relatively easy fix, I'd try that first. If those tires are more than ~4 years old, get new ones at the same time.

Dave