Please help diagnose a whining / rattling sound when AC ON during idling / slow speeds

I have an '07 Tacoma DCLB.

When I'm sitting on lights, or general bumper to bumper traffic situations I can really hear the AC compressor (at least I think its the compressor) turning on and off, powering up for 10-15 seconds and cycling off again.

I recorded the sound on a voice memo from inside my cabin using my iPhone, I hope it's clear enough to make out. At 0:08 you can hear the compressor coming on, and at 0:23 it turns off again.

Some observations:

• When I have the hood open, I don't hear any grinding sounds in the engine bay just the sound you hear in the cabin except maybe slightly louder.
• When driving in general stop and go traffic, when the AC is on, it seems to whine a bit as I accelerate (similar sound) almost as if possibly the alternator is failing? It's a bit more whiny (higher pitch), but it's there.
• The truck has a newish compressor (replaced 2 years ago)
• The serpentine belt was also swapped for a new one 2 years ago/ looks when I checked it good
• No rubber / burn smells
• No grinding noises from the pulleys
• AC blows ice cold
• HVAC motor seems to be working without issues (new model HVAC reistor/pig tail)

Any help on diagnosing what could be causing this would be extremely appreciated, it feels like it is now much more pronounced than it was just 8 months ago. Or maybe it's psychological and I'm just making a mountain out of a mole hill.

Note: Seems I can't upload the file directly as the forums don't appear to support that file type, so I zipped it and uploaded it that way. I hope it's not too much hassle.

 

Anyone?

Is it possible the sound is my alternator starting to die?

 

could be alternator, good way to test that is when its doing the noise unplug the green 4 pin plug on the alternator, if the noise goes away theres your answer.

Also check the intake where it goes through the fender well, those can rub and make weird noises.

 

Thanks for the advice, I will be sure to do that. Will check back with updates later in the day. Cheers.

 

Ok, so I checked the alternator by unplugging the green plug and the "mechanical whining sound" continued. I checked the intake / fender well, etc. and there is no noise emanating from there.

I did a bit more diagnostics, if I can even call it that...

• I had the truck in PARK, with the AC set to OFF. I started revving the engine to about 1500RPM and all sounded right, there was no weird mechanical whine, it sounded healthy.
• I kept the RPMs at 1500, and then turned the AC on, and very quickly (once the compressor engaged) there was a mechanical whine on top of the engine rev sound.
• I continued the RPMS and then turned the AC off, the mechanical whine went away instantly, did this a couple more times just to be sure, and the whine is only audible when the AC is on.
• I also noticed that when the truck idles with the AC on (the sound in the MEMO), the sound appears and disappears when the AC Compressor engages and disengages.

Could this be a clutch/pulley issue directly linked to the AC itself?
I mean, correct me if I'm wrong but doesn't the clutch continue spinning even if AC is off?
Wouldn't the mechanical whining noise always be audible and wouldn't matter if AC was ON or OFF?
Lastly, if the clutch/pulley ceased, then the compressor wouldn't function, and thus would result in a blinking AC switch right? (My AC works fine, blows ice cold... for now)

This is driving me absolutely bonkers. At least at this point, I'm almost certain it has something to do with the AC. I guess at this point, the question is...

Should I be replacing the whole AC Assembly, or possibly just the clutch/pulley?

If anyone has any extra info they can provide it would be extremely appreciated at this point. I scheduled an appointment at my local dealer, headed their way in a week.

 

Whelp if the sound goes away when the compressor is off then its not the clutch bearings, sounds like your compressor is on its way out.