I hear a squealing noise coming from my front brakes

It is an indication your brakes are nearing their wear limit. The squeal tab on one of the pads is just barely dragging on the rotor and vibrating to produce the sound. When you apply the brakes you're deadening the vibration and the sound goes away. As the brakes heat up the clearance between the tab and the rotor increases a smidge and it doesn't drag with the brakes off and stays quiet.