I see similar behavior out of my Ksyrium SLs though not as pronounced as what you're describing. I posted a question on it sometime last summer and the responses were that it wasn't abnormal.

I'm happy with SLs. They're crisp without being too harsh. I have also hit some major potholes with no damage to the rims. The bladed spokes do catch strong crosswinds, however. Also, be sure to order a couple of Mavic spoke magnets, regular cycling computer magnets won't fit on the spokes.