Diagnosing possible alternator whine.

[Expedro]

Gday from Oz. Looking for some advice on diagnosing possible alternator whine issue. I fitted an LED light bar a couple of weeks ago and since then I have had a series of high pitched tones which seem to be coming through the speakers. The first tone doesn't start until I get to 60kms/hr. The pitch of the tone stays the same but rises in volume steadily until I get to 80kms/hr. The pitch then completely changes to a new higher tone, with the volume again slowly increasing until 100kms/hr where it changes to higher pitch again until finally disappearing at about 110kms/hr. The tones can be heard in the reverse order when braking from speed, just not quite as loud.

I'm not much of a mechanic but have done a bit of research online. For the most part the symptoms sound a little like alternator whine. I first tried finding a new and better earthing point for the light bar, but that didn't help. So I completely removed all the light bar wiring and that didn't do anything either. Checked the battery with multimeter and all the numbers seem to indicate the system is charging fine. Tested it without engine running, with running and running with different amounts of load. Each time the alternator adjusted as its supposed to. I even tried adding extra battery earthing points but again no help.

My next step is taking it to an auto electrician for diagnosing. But before I do I would really appreciate what any of you might have to offer. Cheers mates.

 

[Number4]

Sorry you aren't getting much help. So when you removed the light bar completely, the noise persisted?

Do you have anything else electrical added on?

 

[Expedro]

Don't have anything else hooked into the power system. Even after I removed all the wiring for the light bar it continued to make the tones. I also noticed that it makes the same tones even the stereo is off. I went so far as to pull the fuse under the dashboard that supplies power to the stereo and it still makes the tones. Beginning to wonder if the tones are coming from somewhere other than the speakers but even people sitting in the back reckon it's coming through the speakers. Without going to a auto electrician I'm a bit stuck for ideas. And because it didn't seem to make any difference I rewired the light bar back on.

 

[Number4]

That's truly odd. With no power to stereo, not sure how you'd end up with speaker whine.

 

[The Rev]

It sounds like the alternator is on its way out. Not totally converting AC to DC and it is being radiated through speakers. Just an idea. Maybe check ground to alternator as well.