Brake pedal sound

I am getting this sound in my 05 trailblazer ls, and the brakes feel applied half way through (after the sound).

[suramchand]

My brake pedal is to hard and weak brake and create same noise what's the problem??

[bFORCe]

Mine is doing the same thing. Changed my rear brake pads and now its doing this. The brakes work fine and all, no spongy pedal or hard pedal, just that whooshing sound whenever I press on the brake. How did you fix it?