I'm hearing lots of things, which sound like places to begin. The fact 'she' ran so smoothly right up until they did the 35k service told me it had to be something 'they' did at the dealership. I just couldn't come up with anything except the rotation of tires might have caused the vibration.
I have begun paying closer attention to it and this evening, on the way home, it was almost gone. This morning on the way in to work it felt as if the car was surging.
Lexus is recommending I flush the tranny/universal and do the fuel injection/throttle body service. Would these help? Funny you would mention motor mount. During my youth, I had a '67 Chevy with a broken motor mount, young, reckless kids shouldn't drive 327 four barrel carb'd cars but I digress. The engine vibrated, lots more than the Lexus, but vibrated nonetheless. It was the first thought in my mind.
I reckon it's time to setup an appointment and see if we can find out what is causing it.
-JRRRRRR