High Pitched Idle

Earlier this year, I had to have my alternator changed out in my 04 Ford Escape - the local shop installed a re-manufactured part to save me a bit of money (which was fine with me, considering the brand new alternator I had had installed needed to be replaced after a year and a half). For the most part, the car works fine, but when it is idling (especially after a cold start) there is a constant high pitched “whir” sound. I have also noticed the lights dim a bit when more systems are used, but nothing ever stops working. I have had the alternator checked 3 times now, but each time it is charging the car normally. Any ideas what could be causing this? Thanks in advance!

Did they also test the battery?


Whining noises when the engine is cold that get less noisy as the engine warms up are pretty common and often due to drive belt or accessory problems. Here’s some questions to ask your shop.

  1. Is the belt that drives the alternator in good condition? Is there any sign of oil on it?
  2. Is it even the right belt? Does it have the correct number of groves, the correct length, etc.
  3. Is it adjusted to the correct tension? There’s a tool to measure this.
  4. Are all of the pulleys associated with that belt perfectly aligned in the same plane? This can be measured with a special laser-tool.
  5. If you temporarily remove or loosen the belt, does the whining sound go away? Be careful not to disable something critical like the water pump for any length of time.
  6. If you install a different alternator (as a temporary test), does the whining sound go away?
  7. Have the above tests been done for all the other belt driven accessories and idler pulleys?
  8. Has a mechanic’s stethoscope been used to isolate the source of the sound?

One other idea. A battery that is on the blitz can draw a lot more current from the alternator than a good battery. The alternator responds by increasing the magnetic field in the rotor ass’y. This larger current draw puts more load on the mechanical parts of the alternator, and the voltage regulator, and the diodes. Any of those can make a noise under those conditions. So maybe have the battery load tested.

I’ve read about those laser tools to measure if the pulleys are aligned . . .

But none of my mechanic colleagues . . . past or present . . . have one. And many of them have never even heard of it

I’m not sure, but I seem to recall seeing such a tool online, and the price was astronomical

Do any of the pros on the forum have that tool, and if so, what brand, and how much did it cost?

About all I can suggest is that someone listen to various accessories on the engine with a stethoscope or what have you as a whirring sound could be caused by things other than the alternator. Whether that sound is related to the lights dimming I have no idea.

The car is 11 years old so maybe this could be due to a faulty belt tensioner which could cause both a whirring noise and possibly light dimming.
Another possibility could be a power steering pump getting a little noisy; and not unheard of on Fords.

As to a laser tool for pulleys I think I’d pass on that. The cost/benefit just doesn’t work for me.
I seem to recall once while browsing eBay or Craigslist that someone had a used one for sale at about 900 dollars and the stated original price was over 1500. Ouch.


I won’t be buying that in the near future

I can’t justify it, because I wouldn’t use it very often. I can justify an expensive tool, if I know I’ll use it several times each month. Such as my evap smoke machine, which also does just fine finding leaks in intake and exhaust systems

I’ll pass on that one. That’s pretty pricy for what is essentially a couple of laser pointers stuck to magnets.

They also show a pic of the unit mounted onto what looks to be a 110/220 electric motor and refer to “adjusting the pulleys”. All fine and well on a shop air compressor or what have you but adjusting pulleys on a car engine is not going to be easy, cheap, or even feasible.

I check pulley alignment with a length of aircraft aluminum angle stock; a 1.75 a pound at the aircraft tool/material store. Seems to work… :slight_smile:

Thanks for all of the replies! The battery was replaced in February, so I hope that it isn’t the source of any problems it is having. The alternator was replaced ~2 months later - it is under warranty for another few months, so if something is going to fail, my hope is that it fails soon. FIL is an engineer for Ford, so I will ask if he can check out some of the suggestions in this thread before I drop more money at the shop. Not in a huge rush right now, since it is getting me where I need to go - noise just gets irritating after a few minutes at a stop light.

Interesting. Manufacturing an inexpensive version of this laser-tool for pulley-aligning seems like it might be a business opportunity for someone. It does seem just to be a laser-pointer mounted on a fixture, and attached to the pulley by some magnets. For some reason there’s a second one on the other pulley, but that seems unnecessary. You could just look where the laser dot is located. A laser-tool like that would be useful when access for a straight edge is a problem.


Can you please explain your reasoning for the second laser being unnecessary?

It’s normal for an alternator to “sing”, especially just after the starter motor has just put an extra heavy load on the battery and the alternator has to put out extra high current briefly to bring the charge level back up. You may be a little more sensitive to it due to the recent alternator problems you have had.

Can you please explain your reasoning for the second laser being unnecessary?
@db4690 .. if I understand how the laser aligners work in pairs, one transmits a beam and the other receives it. If they both attach to the pulley exactly the same way, and the receiver aperture is in the same spot as the transmit aperture on the other one, then the transmit beam should align with the receiver if the pulleys are aligned. The only other thing you'd need to do is hand turn the pulley's so the modules faced each other. But if you knew where the beam was supposed to hit on the other pulley -- you could figure this out by doing an experiment on a set of pulley's you knew were already aligned -- you wouldn't need the receiver module, you could just look at where the red dot was pointed on the second pulley.