My 'bird makes a loud rattlin' noise when turning on the a/c or heater at idle. Been doing it for years, just haven't bothered to take a look.
Common cure?

Also, what do you guys put out from your battery?
Mine was above 13 for a while, just recently it dipped down to 11.

Thanks.

Is the noise coming from inside the dash?

Is that voltage with the car running?
If it's running, i don't like to see a car below ~13.3. Sounds like the alternator isn't charging. Get it tested and use a test light on the connector to the Alternator. With the key on, at least 1 terminal should be hot.

Remove, clean, and reinstall all the connections from the alternator to the battery. Do the game for the ground connections. It should make (actually - may make) a measurable difference.

The noise is coming from under the hood, but is very loud inside the car, possibly the dash too?

I should just turn the damn thing on and see exactly where I guess. Was hoping it was a common thing to diagnose.

As for the voltage, yes while running, it was always over 13 for me too, then suddenly I started her up the other day, down to about 11.

I've had many an alternator prob. in the past, this delco one lasted 2 years almost, that would suck to replace.

Mine does that too...not a problem.

The AC thing I'm talkin about.

It would most likely be the blower motor it is in the engine compartment as far to the back passengerside as you can get in the engine compartment

if u have a single serpentine belt...the spring loaded balancer (idle gear close to the alternator)...mine rattles slightly from 500-1000RPM but over that its fine..

ive never been able to fix that though...

it does it only when A/C clutch engages...if heater is on but A/c clutch is not engaged it doesnt happen...

is it the same place in urs guys??

The noise is loud though, i'm sure it's not a problem problem, but it's something I'd like to fix!

Sooo why is the blower motor rattling if that's it, old, needs replacement?

I've got the battery on a charger all night. ..
something tells me the alternator is poop'n out.

I think that's where mine is too, and around the same idle range as well, as soon as i hit the gas it stops.

is it like a fast tapping noise?

you could say that

Have you popped the hood and watched the a/c as someone turns the a/c on? Sounds like it's just the compressor clutch kicking in and out, no big deal. 'Fact the a/c clutch cycles on and off when you put your defrosters on in the winter- purpose is, to keep the a/c system from freezing up. It's the same reason why you have to "pass" the a/c positions in order to get to the heater position... when you slide the control from "off" to "heat", the a/c system gets a quick "shot".