Why would a truck with a camper be rejected during the exhaust system inspection?

A truck with a camper may be rejected during the exhaust system inspection primarily if the exhaust does not discharge from the rear or sides. This condition is critical because it ensures that harmful exhaust gases are expelled away from passengers and other road users, minimizing exposure to toxic emissions.

In vehicles with campers, the design and placement of the additional structure can impede the proper routing of exhaust fumes. If the exhaust is unable to discharge effectively from the designated areas, it poses a health hazard.

The other options might point to specific issues, such as noise levels or partial blockage of exhaust routes, but the key reason for rejection centers around ensuring that exhaust gases have a clear, safe path away from the vehicle. This is crucial for maintaining air quality and safety standards, which is why option D highlights the most significant factor in this scenario.