Which condition indicates an issue with parts that hold air?

An audible leak is a clear and direct indication of a problem with components responsible for holding air in the system. When there are air leaks, you can typically hear a hissing sound as air escapes, which suggests that there might be a crack, loose connection, or a failing seal in parts such as the air tanks, lines, or valves. This can affect the overall performance and safety of a vehicle, especially in systems reliant on compressed air, such as brakes.

In comparison, excessive vibrations might indicate balance or alignment issues rather than a specific problem with air-holding components. Visual damage could suggest wear or failure, but it does not necessarily confirm an issue with air retention unless accompanied by other symptoms. High pressure might actually indicate that the system is functioning well if within safe limits, but it does not give a clear indication of leaks or failures in air-holding capabilities.