by Keith Hamburger

Created on: January 31, 2009

There are a wide variety of causes of squealing and screeching under the hood. The most common of those can be quite easy to find and repair. Usually screeching sounds have to do with the parts of the engine that are turned by the fan belts. Alternators, water pumps, belt tensioners and the like, or even the belts themselves are the most common causes of such noises.

Finding the noise

The easiest way to find the source of a noise under the hood is to just listen. You can often identify the location just by opening the hood and determining which side of the engine the noise is coming from while the engine is running.

The next step, once you've determined if the noise is on the left or right side of the engine, is to get your head low to the ground and above the engine to see if it is coming from the top or the bottom. Getting the general location in this manner may be enough to pinpoint the part that is making the noise.

If you still can't find the source you might try using a mechanic's stethoscope or just a short length of plastic tubing. Placing one end of the tube in one ear and pointing it in the general direction of various components can help you locate the exact part that is causing the entire ruckus. Be very careful, though. Be certain to keep away from moving parts. You shouldn't need to get too close, just pointing in the general direction should be enough.

Belt tensioner

Engines with serpentine belts use a spring-loaded tensioner to keep the belt taut. The belt tensioner is a very simple part. All it consists of is a pulley mounted to the block that is pushed tight with a spring. The most common cause of noise in the tensioner is failing bearings on the pulley. If this is the source of the noise you might try a little bit of oil in the center of the pulley but you are most likely to need to replace the part.

Accessories

A similar thing can happen with accessories like alternators, water pumps, power steering pumps, air conditioning compressors and the like. If you've identified the noisy part you might be able to take care of the noise with an appropriate lubricant. Be careful what you use, however, as some of these parts can be damaged with the wrong kind of lubricant. You may need to use oil on some parts and graphite or other lubes on other parts. Most likely, however, you will need to rebuild or replace the failing part.

Belts

Sometimes the noise comes from the belt itself. The belt can be slipping or damaged resulting in squealing. If the belt is slipping you may need to look to the tensioner if the belt is loose. Otherwise you should replace the belt if ensuring it is tight doesn't resolve the noise.

If the noise isn't located in one of the above locations you may have a much more serious issue. Such sounds coming from inside the engine or from the transmission can indicate major mechanical issues. If the noise is coming from the wheels or axles you could have failing wheel bearings, or worse. Unless you are a particularly experienced mechanic, or quite adventurous, any of these sorts of noises will likely require a trip to a qualified repair facility.

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