Car exhaust sounds such as grinding, clanging or unusually loud rumbling typically indicate a problem with the exhaust system, while occasional high-pitched whining noises indicate a badly tuned exhaust system. Holes and leaks in the exhaust system are the most common causes of unusual exhaust system noises, but poor repairs and problems with the system's catalytic converter also cause odd sounds.
Loud rumbling, roaring or grinding sounds usually result when a leak or hole exists somewhere in the exhaust system. Rust eventually causes minor holes in either the exhaust system's pipes or the muffler, which cause moderate rumbling sounds. The volume of the sounds varies depending on the size of the hole. An extremely loud roaring or rumbling sound usually indicates either a seriously damaged or missing muffler or catalytic converter.
A somewhat damaged catalytic converter produces a jumbling sound, reminiscent of marbles or rocks inside a metal box. This noise is most audible during idling, and may not be present at all when the vehicle is in motion.
A high-pitched whining or whistling sound from the exhaust system usually indicates a flaw in design or inadequate repair. Harmonic resonance, a phenomenon that results from the different parts of the exhaust system vibrating at different frequencies, produces this unpleasant sound. This sound does not indicate any mechanical problem with the vehicle, and most service shops or dealerships can eliminate it by properly tuning the exhaust system.