Diagnosing Alternator Whistle

[alvocado]

I have a 1 year old OEM 160amp alternator that is whistling on my '11 Yukon. The whistle varies with RPM and is audible from cold start as well as warm operation. I ran 3 consecutive voltage tests with my Actron and pulled the following data:

 

K0E0: 11.8, 12.9, 12.6

Cranking: 8.5, 8.8, 8.8

K0ER: 14.7, 14.8, 14.8

 

I did not detect any AC voltage at the battery terminals using a multimeter which would indicate a bad rectifier. Any thoughts on how to troubleshoot the whistle including confirming if the alternator is bad would be appreciated. 

 

[Ian Mills]

Those cranking voltages might be a little low but that wouldn't be the alternator's fault. Otherwise those look normal to me.

Is there any play in the alternator shaft or does it feel like the bearing is bad when you spin the alternator by hand?

Also, you're 100% sure the alternator is what's whistling? The power steering pump is another common source of whistling and it's right there below the alternator. Just a thought.

[alvocado]

It's definitely the alternator. I had the pleasure of changing the P/S pump 3 times in the past two months after getting two bad replacements and the pump is finally dead quiet.

 

The whistle sounds like I have a turbo charger on the truck and it's easy to isolate when listening up next to the alternator. I put a stethoscope on it an the bearings sound normal. No noise when spinning the pulley with the belt off either. 

[chem_man]

Visit a real auto electrical shop and have them look at the output of the alternator with an oscilloscope.  That will reveal a lot about the condition of the alternator.