umm...if she's claiming its loud from the engine, she could have punctured a hole in her exhaust, but if it's not related to the engine, it could be any of the numerous plastic mud/water gaurds found under the radiator, and engine, under the fenderwells...just look with a flashlight if something may be getting blown by the wind and forced on the tire (causing a loud humming) or on the road. Try to locate the section of the car that it seems to be commin from, and it will be much easier to help her out. If it happens at idle, id guess its an exhaust leak, but it could be something much worse.