this reminds me of a true story of a local fast fit who had a vw polo in for a wheel bearing noise they proceeded to change the front wheel bearings one at a time but noise still there informed customer its prob the diff so a new gearbox fitted and yes noise still there so they then decided to get there senior technician in from another depot and after road testing the vehicle he informed the fastfit technicians no i wont call them that fastfit fitters , to remove the roof rack and the noise dissapeared, you will be amazed what they can do!