Professional auto technicians often use their sense of smell, touch, sight and hearing to help them diagnose vehicle problems. With a few tips and practice, you can too. In our DIY article series “Use Your Senses to Diagnose Vehicle Problems,” we explain how to use each one of your senses as an effective diagnostic tool. This fourth and final article of the series focuses on how to use your sense of hearing to diagnose problems quickly before they cause a costly breakdown.

Sound Advice

Most of us are familiar with the sounds our vehicles make – the engine cranking over, air rushing past the windows, tires rolling on pavement and that annoying little dash squeak that only happens in winter. Whether you bought your vehicle new or used, it’s a good idea to become familiar with the noises it makes when everything is operating properly so that you’ll know when something sounds abnormal.

Abnormal vehicle noises can provide us with clues to diagnose existing and potential problems. Here is a list of seven common vehicle sounds and their causes. Is your vehicle making one of these noises?

Clunking – Clunking noises are typically suspension related, especially if you hear the clunk when going over bumps or turning at slow speed.

• Clunks from the front or rear of the vehicle can be caused by the following.
  • Worn out suspension components such as sway bar bushings, sway bar links, broken shocks or struts, damaged strut mounts and worn or broken shock bushings
• Common sources of clunking from the front only include the following.
  •  Worn tie rod ends, upper or lower ball joints, outer or internal steering rack bushings, steering shaft U-joints or wheel bearings
• On rear-wheel-drive vehicles, a clunk when putting an automatic transmission in reverse or drive may be caused by the following
  • Worn out drive line universal joints (U-joints)
  • Worn internal transmission parts
  • Worn differential components
•  In rare cases, vehicles with full frames, such as trucks, some vans and SUVs may develop clunking noises from the following two issues.

  • Damaged body mounts or cracks in the frame.

    NOTE: In addition to clunking noises, you may notice changes in the gaps between body parts that previously lined up correctly

Screeching – A loud screeching noise when you start your engine or while you’re driving can be scary. No screech noise is normal so let’s go over what the most common causes are based on when they happen.

• Starts immediately after starting the engine, quiets at idle, then screeches again on acceleration.
  • Loose, worn or glazed drive belt 
• Continually while driving (sound will vary with engine rpm)
  • Bad alternator, water pump, A/C clutch or idler pulley bearings
  • Bad wheel bearings

• Only when braking

  NOTE - May also be described as grinding

  • Disc brake pad metal backing rubbing brake rotor 
  • Brake shoe metal backing contacting the brake drum
• Disc brake wear indicators (may be louder at slow speed in reverse)

Engine Knocking or Pinging – Most fuel-injected vehicles have engine knock sensors to prevent the pre-ignition knocking or pinging noises that were common in carbureted vehicles. But that doesn’t mean your fuel-injected vehicle is exempt from making these noises.

• Defective knock sensor
• Worn pistons (may go away when warm)
• Low oil pressure (Bad oil pump or low oil level)
• Loose flex plate / torque converter bolts
• Loose harmonic balancer pulley bolt (typically loudest at idle)
• Engine connecting rod or crankshaft bearing failure
• Excessive crankshaft endplay (small engine’s idle may slow when pushing clutch pedal in)
• Improper heat range spark plugs
• Engine overheated

Engine Ticking – With the exception of a loose spark plug wire arching to ground, ticking or rattling noises are usually due to internal engine problems. Some of these noises can be accompanied by malfunction indicator light (MIL), a.k.a. check engine light (CEL) or a dash warning light.

• Malfunctioning hydraulic valve lifter
• Faulty variable valve timing actuator
• Worn piston wrist pin(s)
• Exhaust leak or loose/cracked exhaust heat shield
• Normal noise from hot exhaust heat shields cooling down
• Worn valvetrain parts such as camshafts, lifters or rocker arms

Engine Rattling – This noise can be loudest when first starting a cold engine then quiets once the oil pressure builds up. Very loose timing chains can make noise hot or cold and will be louder at idle then at higher RPMs.

• Defective timing chain tensioner
• Worn timing chain
• Low engine oil pressure can cause timing chain tensioners and variable valve timing actuators to malfunction

Hissing – You would be surprised at the variety of reasons your vehicle can make a hissing noise. Here are the most common ones.

• A vacuum leak from a vacuum hose or vacuum-operated component either under the hood (example: MAP sensor hose) or, in the passenger compartment (example: vacuum-operated hot water valve).

• An overheated engine may emit a hissing noise, typically from the hot coolant going into the overflow bottle through the radiator cap.

  Warning: Do not remove the radiator cap when the engine is hot!

• Your air conditioning (A/C) system may hiss if refrigerant is escaping the system, or the A/C compressor has an internal leak.
• A hissing noise may be caused by an exhaust leak. A restricted exhaust system can also make a hissing noise out of the tail pipe during acceleration.
• Coolant leak spraying on hot engine parts or exhaust pipes (may be accompanied by steam)

Popping, Backfire or Snapping – Popping, backfire or snapping noises are the most prevalent concerns auto repair shops hear about from vehicle owners. Here are the most notable reasons.

• An exhaust system leak may cause a mild to moderate popping noise only on deceleration, as excess air is drawn in through the leak and mixes with any fuel vapors lingering in the exhaust system.
• A loud backfiring noise from the tailpipe often indicates that there is an ignition system malfunction (examples: bad ignition control module or fouled spark plug). This kind of backfire may also be accompanied by an illuminated MIL and loss of engine power.
• Loose or worn front or rear suspension parts can pop when turning or going over bumps.
• Popping noises from the engine intake system (air filter box) often indicate an internal engine issue (example: burned intake valve) or problems with the fuel injection system (example: bad mass airflow sensor).
• If you hear a popping noise from under the front of the car when accelerating from a stop or on slow tight turns, chances are your front axle constant velocity (CV) joints are worn out. Most often the rubber boots that protect the joints split and the grease leaks out, causing the CV joint to dry out and wear prematurely.
• A popping noise that seems to coincide with the revolution of the tires can be caused by a loose or defective hub cap.

Use Your Senses to Diagnose Vehicle Problems
What's That Smell? | Sense of Touch | Looks Like Trouble