The IS350 I drove had a tiny bit of "thrum" from the performance tires while on a grooved section of freeway, but otherwise was very quiet.
The reason I'd not recommend the IS250 is that the 350 is very good value and much more fun to drive. Back when the 250 was the only IS available with AWD, I'd have considered it as a strong year-round sedan choice, but the AWD 350 slays it.