I've been experiencing this for awhile. It's not too severe and it's intermittent. I've had the wheels balanced twice and it doesn't occur at all below ~60mph. I don't think it's the wheels since it's intermittent and it's not there at all at lower speeds. The only thing I can think of is that there's some kind of resonance occurring that the suspension isn't buffering out for some reason. It's really odd. The car will be perfectly smooth... then it'll start bouncing... a little at first then worse and worse... then subside and go away only to start again spontaneously in a few more minutes. Thoughts? Anyone else experience this? I've got a 2012 P85 with active air suspension, 19" wheels and ~108k miles.