Interesting...

[4evrwyntr]

I noticed today that when my car is cold it makes a strange noise under the hood at idle on a start. Like a belt.
...

But here's the thing I found out today...
First off, the noise (again, likea worn belt) goes away after a few minutes. And it only happens when I turn on my lights and the engine is cold. ?!?!? Yeah, huh. I found this out today in the work parking lot. Due to my working hours (in my car at 6am-7am, then 3 or even 5 to 6pm), I instinctively turn on my lights as soon as my car is started. But I noticed when I flicked them off, the whistle stopped. Then I repeated the test. I flicked them on; the belt noise started. Off, gone. On, noise.

...

Okay... so I have a couple ideas, but what do you guys think (plus I don't have a clue what a lot of the bits are called - I usually refer to car bits as "that big funny shpaed black piece" or whatever).

[Zapak4eva]

I dont know about hte whole lights issue, but I had a similar problem where my car made a noise only after a cold start. However, my car was in warranty. It was a while back but i believe the dealer told me that they just needed to replace my belt and something else, there had been a recall but nothing major.

[Furious]

hmm maybe the belt is worn, or maybe one of your pullies is starting to seize up in the cold.. this could account for the lights as well , as one part of the belt/pully system could have a problem and could adversely affect the alternator..

just a guess, but worth a look

[Dirty Martini]

This has got alternator written all over it, either the belt or the device itself. Right after starting the car, the alternators #1 job is putting the amps you used to turn the starter back into the battery. Then you tell it you want lights too so now your alternator is making juice like mad. An alternator under load is harder to turn than one that isn't. I would check the belt first for the obvious bad signs:glazing, cracking. If after checking/replacing the belt the problem persists, it's time to take the alternator off the car and have it bench tested.

[4evrwyntr]

Ah. I was thinking it was the alternator as well... except that my car RECENTLY brought the battery back to life (battery was dead when I got it back from the mechanic, I was going to yell at them but I was so happy after not having a car for a month, I didn't care... 80 miles a day and battery is back up to speed)... but I wasn't sure if the alternator belt could go bad. Come to think of it, I've never heard of that (but I'm a car newbie).
Does the alternator have a dedicated belt AND pulley? I know when my water pump blew, I lost a pulley and belt, but that was for something else. Maybe it's just time to replace all the belts...

[drz]

The alternator is driven by the same belt as the water pump. Your alternator may still be bad. In fact, having had to work too hard to resucitate a battery may have caused some damage. Taking the alternator out is a piece of cake. You can go and have it bench tested in an auto parts store.

[4evrwyntr]

Compelling. Would a bad alternator possibly ever damage the water pump?