if he is pulling a BLINKING SES light while this vibration happens, I seriously doubt the problem in in suspension. The only thing that will trigger a blinking SES light is a serious misfire in the engine. I understand where everyone is coming from but I doubt axles are your problem. make sure all your wires are going to the right plugs, clean the contacts on each ignition coil, maybe even replace the coils, it's not a bad idea.