2010 F450 6.4 Doesn't happen often maybe once in 50 miles or so. Usually last a minute before starting to clear out. Worse with heater on, most the time at lower speed. Don't notice any change in running at the time.
This is an indication you most likely have an exhaust leak under the hood. A couple of common places to check for leaks (in order of likeliness) the turbocharger inlet pipes at the back of the engine - particularly the right side at the flex joints, the exhaust manifolds sometimes break bolts and leak at the cylinder heads and the exhaust down pipe where it connects to the turbo.