high pitch whistle

[ternil@union.edu (Lyman M. Terni)]

my 87 8v has started to make a peculiar noise over the past several 
days (since it got pretty cold out) here are the symptoms:

1)Only does it at idle, once up to ~1200 RPMs its stops
2)louder when the lights are on.

So, I'm wondering if this is either a)a belt issue, although the alt. 
belt seems to be alright quality and tightness or b)an issue with the 
alternator itself making funny noise. The alt. still produces ~14v 
according to the volt gauge, which seems to be roughly correct, as it 
is at 12 exactly when the engine is off.

Any ideas?

Thanks,
LT
87 8v