When Brake pedal is depressed squeal sounds

I just bought a Tacoma and when I press down the break pedal a high pitch squeal sounds. Even when you are stopped and the pedal is depressed a sound is made. I think that there is a vacuum leak in the hose and that is the cause of the problem. If any of you have had this problem or know how to fix it, it would be greatly appreciated.

 

I had a work truck that did this (f450 08-10?) the floorboard was damp. turns out it was the oring/seal underneath the boot that connects the pedal to the piston in the master cylinder. the brakes still worked , but it was slowly losing fluid. they fixed it , I think they replaced the entire master/booster.