2008 f350 Buzzing under dash fix **read**
I have been plagued by a buzzing from the are above the glove box for 4 years. Dealer never could fix it. It would start around 40-50 mph but would not be present at slower or faster speeds. It sounded like a loose screw.
There is heat shielding between the exhaust as it travels up toward the engine and the firewall. This shielding is pieced together and attached to itself with metal fasteners. The buzzing is the metal fastener. When I rotated it to make it tighter the noise went away.
I have attached picture of the fastener . Hope this might help others.