On 2007-03-12 09:11:59 -0400, "Travis Marlatte"
said:

Classic symptom of an open alternator diode is fairly loud, low pitch
whine at idle. Increased frequency and lessor volume with increased
RPM. Usually to the point where it is hardly detectable (at least to my
non-dog ears) at high RPM.

Yup, that is pretty much it.

Turns out my AP has a spare alternator in stock, so we can do a quick
switch as a test.