It's a cycling noise coming from the engine bay. Doesn't matter the outdoor temperature. A/C is not on.
Thanks for the help.

 

Have you opened the hood to try and isolate the sound?

 

Is the defrost on? The a/c clutch can/will engage.

 

Sounds like it's coming from underneath the plastic shroud over the intake. Haven't taken it any further.

No, defrost is off.

I'll take another listen this afternoon to see if I can isolate it a little further.

 

Went out this morning and nothing. Even turned the a/c on. This thing's been bugging me for awhile and now it decides to hide out. I'll have to sneak up on it. Maybe temp does have an effect. It was in the 20's when I tried. Stay tuned.

 

Ok, the A/C compressor/motor is the source of the noise when it engages.
First question: Why would that turn on when it's 30 degrees outside and both the A/C and defrost are off.
Second question: Does this mean the compressor is shot or are there other things I can check?

Thanks much.

 

It will come on regardless to maintain cabin conditions. If the noise is from the bearings, then the compressor is on it's way out.

 

It's not a sound I would associate with bearings, though I'm sure I could be wrong. It's more like a fast tweeting sound.

Any other possible causes?

 

Squeaky belt? Usually that's just a stretched/worn belt, or dirt in the pulley grooves.

 

That sounds like a good thing to start with. I don't know if it's ever been replaced.

How easy should it be to turn the compressor? I've been reading up on how this thing works, and it seems I can take a wrench to the central nut at the end of the clutch plate and turn the compressor unit. Just thinkin' out loud.