noise while braking

2008 HHR SS 29k mi. In the AM, when backing the car out of the garage, I have very little brake pedal. Symptom goes away as soon as I start driving. At times, when tapping the brake while driving, I notice a 'whistling' which could be mistaken for the squeal of worn pads, but isn't audible when applying enuff pressure to slow and stop the car. Suggestions? ... tia ..