A driver has complained of a whistling noise in the cab at road speed. The noise changed with road speed and is not affected by engine load or speed. The most likely cause would be a/an

• A. Cracked windshield
• B. Clogged cabin air filter
• C. Improperly adjusted driver's door
• D. Loose dashboard panel

Answer: (C)

Wind noise that grows with vehicle speed and isn’t tied to engine RPM or load points to air leaking around the vehicle’s exterior rather than engine or HVAC components. An improperly adjusted driver's door allows air to squeeze through gaps in the door seal as you move, creating a steady whistle that changes with road speed.

The other possibilities don’t fit this pattern as well. A cracked windshield can cause wind noise but typically isn’t the clean, speed‑dependent whistle you get from a door seal. A clogged cabin air filter affects airflow through the HVAC system, not the exterior wind entering the cab. A loose dashboard panel can cause rattles or buzzes, but a true whistle that tracks road speed is most commonly due to a door seal issue.