I was driving home last night and slowed down for a stop sign and my brake pedal started to make a clicking/popping noise as I applied pressure. Today the same problem every time I apply pressure, and it even does it when I'm at a complete stop,it also losses a little pressure sometimes and it will drop down a little. There is no noise or jerks coming from the wheels, it feels like it's just in the pedal. Is there anyone one out there who can diagnose this problem? Thanks. 1997 Ford F-150 Flareside

 

Update: when I dive down the expressway my ABS light comes on and the problem no longer persist, but when I park it and turn the truck off and drive again the same problem will occur as I described above and no ABS light is on. Come on guys I know someone is out there that can help.