lexusee

When starting the car, before hear a sound like "groan", if barely step on the brake without any pressing gas, keep car moving slowly. In that moment, sometimes, it will feel the front brake pulsing hard and hear squeak sound. Does anyone have this issue? If applying gas, the "groan" sound will hear right away. After that the brake seemed OK. However, the problem sometimes happening when slowing over the speed bumper with setp on brake lightly. My is 2001 RX300. Thanks,

JC