My brakes are gasping when I hit them. Sounds like it's sucking air. I checked the master cyl and the wheel cyls and don't see any leaks. It appears to have a vacuum assist coming off the intake manifold. The hose looks good, I can't see any breaks or wear. The brakes work good , I'm just concerned about this sound. It's a 92 GMC 1/2 ton sierra Any ideas?