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Squealing noise

I have a 2004 Toyota Tacoma with 70,000 miles on it and there is a squealing noise coming from under the hood. It comes and goes, I had the belts replaced and it still continues to happen. Brought it to the dealer and they can not reproduce the problem.

I noticed it when the weather got colder so I presumed it was the belts since they had 30,000 miles on them (they still looked good, no excessive wear).

What can it be?


since changing the belts?

I would say it’s the same.

The noise is not constant, it will happen for a few seconds, then stop and then start. Doesn’t really happen on the interstate, I notice it more when I am driving locally. If I stop the vehicle it stops.

I am 90% sure it’s coming from under the hood since the noise is coming from the front.

Have the belt tensioner/idler pulley bearings inspected. This is done by removing the belt, and then slowly rotating the pulleys by hand. If there’s rough bearing, you’ll feel it.


Okay I’m going to ask a stupid question. I have three belts in the truck, is there a belt tensioner/idler pulley for each belt?

Not necessarily. Some belts have tensioner pulleys, and some don’t. You could look under the hood and see for yourself. A pulley that isn’t driving something (power steering pump, alternator, AC compressor, water pump) is a tensioner or idler pulley.

This is not rocket science, and that was not a stupid question.

More information:

I noticed that I only seem to hear it when I am driving locally. For example if I am driving around 30 to 40 mph and I left off the gas and the rpm’s get to around 1200 I will hear it. When I touch the gas pedal the the rpm goes up the noise stops.

The Next Time It Starts Doing It, Try Turning “Off” (Or “On”) The Windshield Defrosters And A/C

To possibly pick up one more piece of this puzzle, turn both off if either is on. Turn one or the other on, if off, while the squeal is present. These devices engage/disengage the Air Conditioning compressor/clutch and load that belt.

Should this control the squeal in any way, I would have a tech look carefully at the A/C pulley, bearing, clutch, belt, system. The " It comes and goes," makes me think it’s because of an A/C compressor cycling on and off for defrosting or cooling, maybe aggravated by colder ambient temperatures.

I tried that and it didn’t make a difference. Could it be the alternator or the water pump or anything else under the hood?

Surely, As Tester Advised Earlier.

If it does it a idle, you can check with an inexpensive automotive stethoscope or by using a long screwdriver with the handle end in you ear. This can be dangerous on a running engine! Be sure to keep you, tools, anything hanging off of you, out of moving parts and belts. The compressor and cooling fans can start suddenly! Listen to the alternator, water pump, air pump, A/C compressor, idler pulley and belt tensioner hubs, etcetera, while it’s squealing and not squealing. You should be able to tell which component bearing is noisy.

A stethoscope is good to add to your tool collection (they work great!) and it will give your neighbors something to gossip about.

If this doesn’t help, at least you’ve impressed your family and friends and had a little fun, too!

It doesn’t happen when the vehicle is idling.

Could it be the alternator or the water pump or anything else under the hood?

Had a similar problem not long ago. Like yours, my squeal went away when rpm’s increased. I had other electrical issues though. It ended up being the alternator.