need some help here. diving car at 55 plus i have a rhythmic hum or vibration.it only does it with foot on accelrator if you let of it stops.i took drive shaft out u joints look good replaced during build of car about 3 mnths ago.i even swapped shafts with dads dart sport still same.got new wheel vintiques 15 inc ralleys and bf goodrich tires from summit. i also have slight howl when let of accelrator. any ideas what this could be?