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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 15578
Experience:  Have owned a repair shop for 25 yrs.
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Why does my new alternator whine? Is there a draw on it already?

Customer Question

New alternator installed has a whining noise. Sounds to me like there is a draw already on the alternator. There are three wires going to the alternator. One red going to the back of the alternator and a red and brown going to the side of the alternator in a black connector. If I unplug this black connector amp draw/whining goes away. What could be causing this whining sound? It basically sounds as if there is a draw on the alternator already.

Submitted: 6 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 6 years ago.

tims auto repair :

Hi, is the battery good?

Customer :

Yes tested good

tims auto repair :

Ok, are you getting the alternators in the same place?

Customer :

Yes, they are brand new units not rebuilds. Replaced alternator 3 times

See I am an auto mechanic in engine repairs not electrical, so feels funny asking questions but this has me puzzled

tims auto repair :

Ok..you need to load test the battery with the car not running. Then load test the charging system with the engine running

Customer :

Did a load test on battery with a hand held load tester and checks out good

tims auto repair :

Does the battery run down after it sits?

Customer :

No

tims auto repair :

Ok

Customer :

Battery holds about a 12.62 charge

tims auto repair :

Under load?

Customer :

No just sitting, not started

tims auto repair :

I mean when you put a load on the battery with the load tester, most testers will put a 100amp load on the battery

Customer :

If I use the load tester that goes right to battery terminals it pulls down to about 11.2 -11.4 and it is a 50amp load tester

tims auto repair :

Ok, does it start well?

Customer :

Yes, strong starter. Sounds healthy. Powerful start

tims auto repair :

Ok

Customer :

See it is not like a bad bearing sound. It is a whining electrical sound

tims auto repair :

How about when you load it for 2 seconds with it running?

Customer :

Honestly did not try that

tims auto repair :

Can you try that?

Customer :

The alternator sounds as if AC, rear defroster, wipers, headlights and all accessories are on

I can. If you give me about 3 minutes I can try that and let you know

tims auto repair :

Ok, don't hold a load too long

Customer :

Ok here are the results

13.8 in drive and I even did in gear and that is 12.6

No accessories on either, except hood light

tims auto repair :

It seems to be operating correctly. How many volts running with no load?

Customer :

Yes it seems to be doing everything right except the whining sound is horrible

tims auto repair :

How many volts with no load?

Running

Customer :

Around 14.4 - 14.6

Maybe even 14.8

tims auto repair :

Ok, when you unplug the regulator plug the whine completely stops?

Customer :

Yes

tims auto repair :

Ok...I think this may be a bad batch of alternators. Sounds as if the front bearings are bad. There would be no reason for this

Customer :

The brown wire from regulator goes to fan fuse relay and the red goes down around to starter

tims auto repair :

Even under a load

Customer :

It is no bad bearing

tims auto repair :

The red is supposed to go to the switch

Customer :

I did a test with an ear probe and there is no noise; barely with the regulator wire unplugged. Just only while plugged in like it is under a load

tims auto repair :

The brown to the charge light

Customer :

I don't have a light gauge

Camaro rs 305 engine tbi

Red goes to what switch? According to wiring diagram it goes to starter. Here is the diagram

tims auto repair :

Let me switch to a different format, I will send you a diagram

Customer :

I have a diagram

tims auto repair :

The bearing has no pressure on it when it is unplugged and not charging

Customer :

So how can it be a bearing

tims auto repair :

Well, under load the electromagnets pull on the ohmeter putting pressure on the bearing

Customer :

It is an electrical whine, not a bearing noise

tims auto repair :

After you start the car, even if nothing is on, the alternator will be under a load until the battery is fully charged from starting

Customer :

Yes, but the noise is there always even after driving vehicle for 2 hours. See it never did this before, just started recently and I only heard the noise if say defroster headlights and rear defroster and wipers are on

tims auto repair :

Charging System Wiring Circuit (VIN E)

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Customer :

But now I hear it with everything off

tims auto repair :

Let us try an alternator from a different place

Customer :

Well I recently paid 120.00 for this one and they are brand new, not rebuilt ones and all three from three different stores, but same store name

tims auto repair :

I think its a bearing

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