At least I am not alone with this issue.
My 2013, 46k mile, is300h is behaving in the exact same way - also seems to be coming from the front left wheel and like Ken has said it is very annoying.
I can hear the sound when I am driving along the motorway at 70mph, just have to pass another vehicle and the sound is reflected back from the vehicle I am passing.
Other than this issue I cannot fault the car at all, it is my first Lexus and I would like to think I will continue to stay loyal to the Lexus brand.
My car is due a service next week at Lexus, let's see what they have to say about this. Will Lexus Relax cover this issue in the future?