By January 1949 GM realized there was an engine noise in the new late 1947 Advance Design cabs that needed correction. If a truck customer complained, the dealer was given a solution by modifying a part from a Chevrolet car.
The problem was engine noise entering the cab through the horizontal accelerator rod where it touched the floor hole. On many early Advance Design models there was not yet a pocket to hold a felt floor seal and insulate this rod. Metal to metal contact was inevitable.
The enclosed article is from a GM product service bulletin issued January 31, 1949. It was sent to all dealers.
Note: It is doubtful if all this work required of the dealer in the bulletin was ever very successful. The real noise problem was actually from attaching the back of the accelerator pedal to the accelerator rod. Metal contact here brought noise into the cab and then to the floor where the accelerator pedal made connection. By 1951 a new pedal to rod connection was used (like the car) and the problem was corrected.