2003 Elantra. This noise confuse me for a long time. When I step on the brake pedal lightly, the groan noise comes on(soudes like water boiling). But when I release or firmly step on the brake, noise's gone. The noise sounde like coming from inside car because I can not hear the same noise outside. Only when I sit inside the car, I can hear it. I checked egine, front end, brake, but nothing wrong was found. Someone got the same problem. Any ideas??