I have an 02 IS 200 Sport - 39k miles that has developed a "rumbling" in 6th gear at 60mph plus.
It feels a bit like out of balance wheels and is coming from the rear of the car, it can be felt in the cabin.
I don't think it is wheel balancing as it only makes the noise / vibrates in 6th and not in any other gear or when coasting only when accelerating, gets worse around 80mph.
Feels / sounds a bit like the noise you get on certain road surfaces - but does it all of the time.
Anybody got any ideas as the warranty runs out end of March and I want to sort it before then!!