Jonathan Goodish writes:

I know that this is another frequent topic, but I'm hoping that someone
can help narrow this down for me.

I have a rebuilt Chrysler alternator (from Electrosystems) on my
Cherokee that was installed about 400 hours ago. However, I am
experiencing alternator whine that varies with engine speed, but which
disappears completely when I turn off the alternator side of the master
switch. In addition, increasing electrical load seems to make it worse.

You could have lost a diode. There are 6 main diodes, usually molded
into a unit.

If you have a friend with a portable oscilloscope, it's an easy test:
load the alternator and look at the waveform. You'll see the chunk
missing as compared to http://www.medar.com/images/3phase5.gif

Or pull the alternator [disconnect the battery ground FIRST, please..]
and take it to an alternator shop. [NOT a chain auto parts store
who has an alleged tester.] They should be able to spin-test it.
AFAIK, having a test done by a non-FAA-anointed shop would be legal.
(Having them fix it, of course will get you sent to Gitmo..)

http://www.windstuffnow.com/main/3_phase_basics.htm

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