Every time I have heard this noise in the past it meant a shorted diode and
a soon-to-be kaput alternator. I had one once go up in a plume of smoke.
Problem is, it doesn't always make the noise. Of course, it sings more at
certain engine speeds but sometimes it is not there at all.
I put a digital volt meter on and have over 12.5v first thing in the
morning. As soon as I start it, I get 14.4v and, after a while, I see 14.5
or so. Turning on the lights drops it to 14.1. In other words, other than
the noise, no symptoms. I plan to clean the battery posts in a minute, just
because it hasn't been done in a while. Any other ideas?
Never attribute to malice that which is adequately explained by stupidity.
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