I was driving home from work a couple of weeks ago, and I turned on the defroster. A minute or two later, at a stoplight, my alternator suddenly began to make a pronounced whirring noise. The noise sounds remarkably like supercharger whine. Which is cool. But I have a feeling that it means bad things. Which isn't cool. It increases or decreases in volume, depending on how much electrical demand there is (rear defroster, headlights, etc.). It also speeds up or slows down as the engine does (higher RPM, higher pitched noise).

So it has been a few weeks since then, and I can't tell that it'* gotten any worse. Right now I don't dare to drive it more than back and forth to work (I can make it the distance to work on a dead alternator, if it comes down to it).

Does anyone know exactly what the noise is, or means? How much time do I have? OR, is it just an annoying, harmless noise?

TIA for any information or wisdom you can share on the subject...

Put a screwdriver handle against your ear, and the tip near the bearing on the back side of the alternator (while the car is running). What do you hear? It'* probably what you suspect. How are the volts? Headlights dim at idle? If the noise changes with electrical demand, it'* that little bugger. Consider changing your battery at the same time.

Yeah, I forgot to mention that the headlights and interior lights do dim at idle (or at any speed with the rear defrost on).

It'* really really nasty cold out right now, but i'll try that screwdriver test some time to confirm.

It should throw a light on the dash when it finally dies - right? Is my alternator in a temporary state of half-life, that it'* not quite dead enough to throw a light? Creepy.

No it wont throw the light untill its dead. But if it is the bearing better to change it out now and have the bearing fixed to let it burn out?

Check the voltage at the battery with the car on and off and note the difference. Also if possible take the belt off the alternator and see if it spins freely. A lot of times the bearing in the back will go out, happening to mine. I've had a bad bearing that will only squeek if you spin it by hand slowly and its still lasted 4+months. If you're mechanically inclined most alternators have a rebuild kit you can buy for probably 1/2 of the price of a new one. The thing is 95% of the alternator never sees wear so realistically when you buy a new one you're paying for 5% of the parts that broke in yours. I've never dealt with one myself but I have a friend that says its cheap and easy, maybe check it out.


Hey since his question seemed to be answered for the time being I thought I'd chime in on the same question. Not technically thread hijacking right? Actually I'm fairly confident I know its the alternator but its interesting symptoms. The car seems to run fine, and has been for quite some time. I say it "seems to run fine" simply because its a Ford Focus, so surely there is something wrong that I just haven't found yet. Other than the hidden defects, sometimes at idle the lights will flicker just ever so slightly. The lights flickering isn't so strange as it is the fact that the backlight on the stereo flickers too. Ya know that stock backlit LCD display for the time? Yeah, that'll flicker. What does that take, 0.5v?? Also at idle if the window is already up and I press the up button the engine will shudder. Happens every time, like the alternator is just too much for the tiny little engine. No obvious noise is comming from the alternator so I believe its going to hide its death until I'm going 70 on the freeway. Any idea other than the ones I've presented here; Ford and/or alternator.

Woah... Is it possible to just fix the bearing, rather than get a whole reman. alternator? I was thinking that I had to replace the whole thing, and that they were pretty much not serviceable by backyard mechanics.

If indeed this can be done, how would I go about doing it?

Well I'm running around the house and heard my computer ding that I had an email so I did a quick search and came up with: http://www.alternatorparts.com which might be a good place to start. Check with them, I noticed they had an alternator upgrade with no core charge, if you want to just replace. They also had a blowup of each part and a cost. I'm sure they have kits available for the most common replaceable parts. I guess calling your local parts depot or a good search online will come up with a few kits. compare that to the cost of a new one and the work involved to see if its worth it. and yes, you can just replace that bearing but since you're in there might as well replace the other couple parts that see wear. Good luck!

BTW that rear bearing for GM is listed for $2.99

Yes, at one time you could buy a rebuild kit complete with bearings and diode trio (regulator). I'm not sure if you still can? but you can buy bearings for anything, try bc bearing. To do it remove the alternator, remove the end bell, the bearing will be pressed onto the shaft you'll need a bearing puller to take it off and a bearing heater to put it back on. If you only do the rear bearing you can leave the pulley on but if your going through the hassle you may as well do them both?

Its been a while since I've done an alternator, I should take one apart and do write up to show how easy it is.

Happy BC anniversary! It'* a year since you registered, and also my birthday woo hoo!

Might be dying, i'm not sure how easy it is to reman them, but a $3 kit would save a lot of us a lot of money...