One day this summer I scraped underneath my car and it started unusually vibrating. When I turn the air on it immediately starts to vibrate and when the air is not on I can feel it when im at a red light I can feel it through my brakes like a fun is running or something. So could be the engine? Transmission, radiator fans, or possibly I need a front alignment checked. Also, I have had this checked this summer and the man said he couldnt hear it but it still is there? Wat is it?