KNKGS400

Start recently to notice that my gs400 when driving around 20-40mph the brakes seems to squeek like hell out of the blue and when you steep/tap the brakes it goes away...again my brakes are fine so i don't know why i would be having this noise not all the time probalry 7 out 10 times during the day enough to be a problem but not enough when i bring up to dealer it's not there..Someone told me my shims in the front brakes can be broke>? again car breaking fine just very bad squeek like noise. thank you