My rear brakes are making a groaning noise when I stop. It was intermittent before but now it seems like every time I stop. It groans right before I stop. Sounds like they are wet, but they're not. Toyota inspected them and said they are fine. Any idea what the noise is or how to get rid of it. It's more annoying and embarrassing than anything else. Its a low "groaning" noise that sounds as if the brakes are slipping or something, but braking performance isn't effected. Any ideas???