Whining noise: alternator, compressor, or pulley?

Vehicle: 2007 Honda Accord coupe EX

Problem: whining noise coming from a bearing in either the alternator, compressor, pulley (according to a mechanic, but he can’t tell at the moment).

Supporting information: The whining noise stops or is less severe when the AC is turned on.

Troubleshooting done so far: replaced o-rings on power steering pump.

Is there a way to diagnose if the noise is coming from the alternator, compressor or perhaps a pulley?

I have used a mechanic stethoscope to try and diagnose bearing noises before. Unsure if it would be as helpful with a whine. Does the whine increase / decrease when turning the wheel while the vehicle is stopped?

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most effective way is to take off the belt and spin each pulley by hand- checking for resistance and unnecessary sideways or front/back movement.

This probably should have been done when the p/s pump o-rings were replaced, especially if the o-rings were replaced to fix this whine.


My GUESS is AC clutch.

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The inlet o-ring on the V6’s from that era is known to fail, so it might have needed doing anyway.

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Thanks all for the answers.

I’ve tried using the stethoscope and it seems that the sound is slightly stronger on the compressor than the alternator. The whine seems to decrease a bit when the wheel is turned (while the wheel is stopped).

I’ll try to the approach of taking off the belt and assessing the pulleys by hand.

AC clutch…will look into that. Hopefully that’s cheaperthan replacing the entire compressor.

Yeah, the o-rings looked worn so I’m happy that they were replaced in any case.

Just an idea, but if you did not replace the belt tensioner, it’s old now and won’t keep the proper tension. Three years ago on my 2006 Nissan, I was still getting noises after just replacing the belt. Replacing the belt tensioner fixed that, and also smoothed out the car’s engine at idle. Still running great today.

Much appreciated.

I noticed that the autotensioner pulley is moving up and down significantly.

A worn out serpentine belt could cause it too. It’s usually possible to completely remove the belt and start the engine, letting it idle for 10 seconds or so. If that prevents the noise you at least know it is something to do w/the belt or something on the belt loop. Caution: removing the belt might prevent the water pump from working, so only do this on a cold engine and only for a few seconds.

If it’s moving a lot then replace it . It generally should not move at all if it’s good .

Thanks for the suggestion.

I removed the belt and inspected all of the pulleys. None of them made any loud noises when they were spinned by hand, so it doesn’t appear to be the bearings on the pulley that’s making the noise, unless they only make the noise when they are spinning really fast. The auto tensioner pulley showed some signs of wear and tear e.g. black scruff marks. The belt seemed fine. I did not see any signs of wear and tear on the belt.

I put the belt back on and turned on the car and investigated further with my mechanics stethoscope.

I noticed the whining sound starts as soon as the ac fan (at the front of the car) turns off. When I turn on the ac then the sound disappears as the fans turn on, however, even with the ac still on, the sound reappears when the fans stop spinning.

The sound seems to be coming from the right side of the compressor. This is where I biggest difference in the intensity of the sound seems to be i.e. when turning the ac on and off.

You can’t determine the condition of a serpentine belt by visual inspection anymore.


Wow. Guess, I’ll have to buy a tool.

You can get two free.



nice. [quote=“Tester, post:15, topic:147153, full:true”]
You can get two free.




The tensioner is basically a metal spring that after 12 years of use has suffered metal fatigue, and is not applying the proper pressure anymore. This can cause some misalignment and stress the other components. If you can change it yourself, a good Gates one can be had for $70 or so. I am sure you will notice an improvement.

Yeah, I bought one, oem for around a hundred dollars. Will try replacing the tensioner this weekend as well as the belt.

Good stuff. Hope it goes ok. On my Nissan it was a little awkward to get at, but doable and resolved my belt issues. Sometimes you can find a Youtube video of the job being done on your car model. Sure enough.

Yeah, I replaced the auto tensioner and it did not solve the problem. The noise is a little bit reduced in intensity but it still persists especially while accelerating the car. Using my stethoscope, I can’t tell if it is the alternator or compressor, since the noise is heard at both of these locations.