One way to diagnose car trouble is by performing a simple noise test. Clicking, grinding, humming, squeaking, rattling or squealing sounds are all indicators that a car may need to be serviced. Additionally, conducting a simple smell test can help diagnose car trouble. Sweet, sulfurous, burning, or musty odors are all signs that there may be something wrong with a car.
Rattling sounds could mean problems with the steering or suspension. Checking for worn plastic or rubber bushings between metal components, and replacing them as needed can solve the problem. A clicking sound when turning the wheel is a sign that the axle shaft is going to fail, and the car needs serviced immediately. A humming sound that gets louder with speed likely means a bad wheel bearing. A squealing sound from under the hood right after startup could mean a loose or glazed belt, and only goes away if the owner tightens or replaces the belt.
Alternating thumping sounds from one or more tires at low speeds is of less concern. This sound is a sign of flat-spotted nylon-cord tires and usually goes away as they warm-up during the day. Replacing the nylon-cord tires with steel-belted tires can make the sound go away.
Two smells that indicate potentially dangerous problems are a burning carpet smell and a rotten-egg smell. The burning carpet smell means the brakes are hot, and may soon get stuck. A rotten-egg smell means dangerous exhaust or emission system trouble. Both smells mean that the car requires the attention of a mechanic as soon as possible.
A musty, mildew smell is far less alarming. Water is likely stuck in the air conditioning and heating ductwork. Running the fan on high for a few minutes can fix the problem.