Does the "shake" only happen in Sport Mode? If it does.. they are going to say its normal. If it is in Sport Mode.. next time you feel the shake.. press the TC button and I bet you the shake will disappear.
It happens in any mode. I noticed in standard mode so tried in sport mode and still was shaking. I tried hitting TC button and shake was still present. Basically in any setting I put it in I have the shake from 55mph and on up.