Well, they're frustrated about brand new Lexus, yours is 14 years old. There are any number of things that can cause a vibration on a car that old, worn bushings, bad shocks, bad springs, bent wheels, bent driveshaft, tranny mounts, engine mounts any number of things.
They are REALLY sensitive to misbalanced wheels, I'd start there...
They're also really sensitive to tires and need a good round high quality tire to get the smooth ride...