My experience with these tyres is the same as Mark's.
Usually tyres get a little quieter in use as the edges wear and the tread depth reduces, so the ruibber blocks 'squirm' less under deformational loads.
I'm at a loss to explain your symptoms though.
Are you confident that it's road noise and not wind noise? If it could be wind noise, have you checked your underbody panels are intact and firmly fixed? Are the driver's window door seals correctly seated and nothing is sticking out into the airflow?