What is this noise?

[tflux]

I just bought a 2002 Chevy Suburban with 166,000 miles. There are quite a few things that need to be fixed. And here is one that I can't figure out...

Anytime the key is in the "run" position, I hear this intermittent squeak, or chirp, or grind, etc. It sounds like the blend door is moving, but its louder. It happens every 20 seconds or so, like clockwork. It always does it no matter if you are driving, idling, or engine not running with the key in the "run" position.

 

It "seems" to be coming from behind the passenger airbag, or behind the glove box. Somewhere back there.

It doesn't matter which discharge location is selected. The sound frequency or pitch doesn't change. It doesn't matter where the temperature control is. It doesn't matter what fan setting is selected.

Chimes are working properly.

The noise happens even when the fan is set to "off".

The noise seems to be completely independent of everything else. Nothing I do changes the sound, pitch, volume, etc.

To me, it sounds like a blend door is grinding. But the blend door is working properly. All settings (floor, floor-dash, dash, floor- defrost, defrost) work properly, and the blend door is very quiet when it changes settings.

 

It is quiet enough that i can't hear it while I'm driving at highway speed, but it is very noticeable when idling.

If searched and searched, and I cannot figure this out.

Can anyone help me with this one?

Thanks in advance!

[kstruckcountry]

You could try pulling fuses for the HVAC and maybe track it down that way. Could be a hard thing to nail down.

 

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