Help with diagnosis

[Murray Nesbitt <murrayn@home.com>]

Can anyone help me diagnose what might be wrong with my 97 GLX,
40090km (90 km out of warranty :-/)?

Started the car, immediately noticed dashboard lights seemed dim.
Checked to make sure they were set to the highest setting.  Noticed an
unusual noise coming from the engine compartment.  Popped the hood, and
got out to check the noise, noticed an unusual smell, sort of electrical
in nature.

The sound seemed to be coming from the area around the alternator.
When facing the front of the car, the metal thing just above and to
the left of the alternator was visibly vibrating.  In this 'thing'
is a threaded hole where a screw could be, but there is no screw.
What is this thing, I couldn't find it in any diagram in my Bentley?

One other thing I noticed was that the engine was idling quite a bit
higher (around 950 rpm compared to around 650) than usual.  When I revved
the engine, the dashboard lights remained dim.

No 'check engine', alternator, or any other warning lights came on during
my drive.

Finally, when I locked the car, the alarm horn gave a *really* muted beep.
Other than the dashlights and alarm horn, the accessories seemed to be
working fine.

Any ideas what might be wrong, or worse, what might be going wrong?

Murray (hoping it's just the dreaded 730-day stock battery)