1990 jeep cherokee limited making humming noise

I just got a 1990 jeep cherokee limited edition in GREAT condition...(i dont know much about cars) but the previous owner got a new head gasket, flushed all fluids, new tires, brakes, etc. anyway as i'm driving it obviously i'm gonna come across some issues. I hear a humming noise in the front right side of the car when i tap the brakes sometimes and this guy had his ABS system just replaced back in july of last year. I read on a forum it might be a vacuum leak? is that a possibility? also today i noticed that the brake and anti lock light keeps flashin on and off randomly? anyone have an idea whats going on with that? i think i'm gonna go to a jeep dealer to get a diagnostic test done on it.