My two year old AWD LS460 is making a loud thumping noise over even the smallest bump on the road. I feel as if the rear suspension is totally ineffective. My car has air suspension and the sport, regular or comfort suspension modes make no difference to the rear suspension. The car has only 6500 KM (= 5000 or so miles) on the clock and I am very disappointed by this. Has any of you experienced a similar problem and are there any TSBs out there on this issue? The only thing I have got done recently was changing to winter tires and resetting the tire pressure monitoring system.