Chirping or Squealing Sound From a Wheel While Driving
A cyclic chirping or squealing noise coming from the vicinity of a wheel often indicates a wheel bearing or axle bearing that is failing. Usually the noise will change with the speed of the vehicle, and it may come and go at various speeds. This noise should not be ignored because if the bearing fails, it may cause the wheel to lockup or come loose from your car!
Don't confuse wheel bearing noise with scraping, groaning or creaking noises that may be coming from the brakes. During damp weather, moisture causes the brake pads to swell slightly. This may cause the pads to drag slightly, creating annoying groaning or creaking noises until the pads heat up and dry out.
A clicking noise from a front wheel that is only heard while turning usually indicates a bad outer constant velocity joint that is failing.
Metallic Scraping or Grinding Noise When Braking
Brakes sometimes make groaning or creaking noises when the pads are damp, and some types of brake pads (particularly semi-metallic pads) may squeal or squeak when they are cold. But as a rule, the brakes should be relatively quiet when they are applied. If you hear metallic scraping or grinding noises when braking, it probably means your brake pads are worn out and your vehicle needs a brake job now. Don't delay because worn brakes may not be able to stop you vehicle in a safe distance. In fact, if the brakes are that badly worn, there is a risk the friction material that's left on the pads may separate from the backing plate, possibly causing the brakes to fail. Metal-to-metal contact is also very damaging to the rotors.
Hissing Sound from Engine Compartment While Driving or After Driving
If you hear a hissing sound from the engine compartment while driving or after turning the engine off, it may mean your engine is overheating and/or leaking coolant from the cooling system. Check the temperature gauge or temperature warning light to see if it indicates a overheating condition. Do not continue driving (especially if you see steam) as severe overheating can damage your engine.
Stop your vehicle and carefully open the hood. Look for any evidence of coolant leaking from the engine, radiator, radiator or heater hoses. If you see steam or smell a sweet odor, it is antifreeze leaking from the cooling system. Do NOT open the radiator or coolant reservoir cap until the engine has cooled down, and do not add coolant until the engine has cooled.
Note: Adding coolant to a leaking cooling system won't accomplish much because the coolant will leak back out. Adding a can of cooling system sealer such as Bars Leak or a similar product may slow or stop a small leak, but a large leak, leaking water pump or hose will continue to leak even with sealer in the system. The leaky part needs to be replaced.
Clicking or Tapping Noise from Engine
Engines can produce a lot of noises, but a metallic tapping or clicking sound means your engine may be low on oil, or is not developing normal oil pressure. The clicking noise is coming from the valvetrain. If oil pressure is low because of a low oil level in the crankcase or a problem with the oil pump, the hydraulic lifters that open and close the valves may collapse creating an increase in valve lash. This is the noise you hear, and it will be coming from the vicinity of the valve covers on top of the engine.
Stop the engine, let it sit a few minutes (so the oil can run back down into the crankcase), then check the oil level on the dipstick. If low, add oil as needed to bring the level back up to the full mark. Do not overfill the crankcase with oil. Also, check the engine for oil leaks. Old valve cover and pan gaskets, or leaky crankshaft end seals can allow oil to leak out of the engine.
If the noise does not go away, and/or the oil pressure gauge or warning light indicates low oil pressure, it's not a good idea to keep driving your vehicle. Loss of oil pressure can cause extensive and expensive engine damage.
Other engine sounds can also mean bad news. A deep metallic rapping noise can be caused by worn connecting rod bearings, and may indicate your engine has reached the end of the road (or will soon!).
If you hear a metallic knocking or clattering noise that only occurs while accelerating or when driving up a steep hill or pulling a load, your engine is likely experiencing detonation, a potentially damaging form of erratic combustion. Detonation can be caused by a buildup of carbon in the combustion chambers, low octane fuel, engine overheating, an EGR system that is not working, over advanced ignition timing, or a defective knock sensor.
Exhaust Roar While Driving
If your exhaust system has a leak, you will hear exhaust noise coming from under your vehicle that is loudest when accelerating. The noise by itself won't hurt anything, but it does mean your exhaust system needs repairs (probably a new muffler or pipes). The dangerous part is if the leaking exhaust gases, which contain carbon monoxide, get inside the passenger compartment. Carbon monoxide (CO) is a silent killer. It takes only a small amount of carbon monoxide inside the passenger compartment to affect your alertness, ability to concentrate and react to changing driving conditions. As little as 0.08 percent carbon monoxide (that's only 800 parts per million) can cause dizziness, headaches, nausea, and bring on stupor in two hours. A one percent concentration of carbon monoxide can kill a person in less than three minutes!
You should have your exhaust system inspected and repaired as soon as possible, especially during cold weather when the windows are rolled up and the heater may be recirculating the air inside the passenger compartment. Exhaust components that typically leak include the exhaust manifold gaskets, cracks in the exhaust manifold, exhaust pipe connections, pipes that rust through, and mufflers that rust out.