Strange gurgling sound from the vent grill under the windshield - please help to identify and fix

Tough one.
The fan is beneath the cabin filter, behind the glove box.

Or, it could be a stuck vent door or even a bad pump

 

Since the cabin fan is set to off, I'll suggest the HVAC door that controls air flow direction is malfunctioning. Put your head down near where the front passenger's feet would be and see if its louder down there. Second suggestion: CD player is malfunctioning.

GOOD LUCK!

 

each air vent position on the hvac controls has a motorized door to open and close air to the windshield/dash vents/floor, as well as recirculate vs fresh air.

most of them require dash removal to get access to. the service manual has the repair proceedures.
they don't 'run' constantly like a fan, but when stuck, keep making a sound as the motor tries to move them.

 

My first guess would be a fault in the CD player/ changer- does yours work? Maybe try locating and removing the fuse for the CD player.

It could also be a air door in the HVAC, but usually when one of those goes bad it makes a sharp clicking or snapping sound. One way to narrow things down is to turn the blower on low, then change one thing at a time and see if it affects the noise. First temperature full cold then to full hot. Recirculate on then off. Lastly mode: dash vent to heater to defrost. If the noise doesn't change as you are manipulating the controls (and the airflow changes as you command it0 then your problem is not in the HVAC.

 

The gerbils are trying to get out

 

Sounds like the hvac door. Mine does it to but not that bad. The noise is the loudest down on the floor by the gas pedal behind the big plastic cover under the radio.

But talking about the front air dam water vent next time you change the spark plugs good time to clean that out. Just stick a hose down its 2 vents and flush it out. You can check it now by filling up that dam with a hose its vents out the back of both front wheels. Should have strong stream of water coming out behind both front wheels.

It may have alot of debris in it especially if it lives outside and not garaged. Mine is garaged and still pretty funky in there.

 

I haven't listened to the 'streamable' link, but if it's a sound like it could be gerbils and the car is a Gen 2 (or Gen 1), try this thread on for size.

 

What was it

 

I would suggest taking your video camera under the dash to watch what the air door linkages are doing. You could compare to the video attached in this post.