I am also having this problem with my IS 300. It squeaks at lower speeds, loudly and irritatingly to such a degree that people look at the car as it passes. I note that there is a lot of discussion about brakes. I have been monitoring my squeak and it happens randomly but regularly mid drive without an application of the brakes. It doesn’t get worse or louder when the brakes are applied. It has turned what should be a great car into something that sounds as if it’s an old banger. I am considering getting rid of it unless someone can suggest a fix!
