I know what you're thinking already "Great, another strange noise post", I apologize up front for that. I have an 06 A4 FWD 2.0T that has started making an odd noise in the area of either below or behind the glove box. It sounds like a gurgling/vibrating noise that seems to go away when I step on the gas. Putting the car in park makes the noise temporarily go away but it comes back. No codes stored in the computer and the car runs just fine. Took it to the dealer and they said nothing was wrong however, the car hasn't always made this particular sound. I changed the blow off/out valve which I really thought was the issue as it seemed to be in the area of the noise but it had no effect. I double checked with my OBD and still no codes present. Any configuration of the air conditioner has no effect on the noise either. Any advice would be greatly appreciated.

 

Try seeing if you can burp any air out of the cooling system. You say the noise is behind the glovebox and it makes me wonder if there's an air pocket in the heater core. Since the heating system is passively in parallel with the engine's cooling system, this could happen (I'm kind of reaching here but...). Crank the temperature on the climate control all the way up while you do it and see if you can burp a bubble out.

 

How would I go about "burping" the system??

 

There should be a bleeder ports on the heater hoses near the firewall. DO NOT OPEN THEM when the engine is hot. You can probably gently squeeze the associated heater hose until a little coolant started to come out. HOLD the squeeze on the hose as not to let air come back in, tighten the bleeder port back (just snug it as most are plastic), then release the grip on the hose. If there are two ports, do them both. Check the coolant level in reservoir and drive it to see if the gurgling had gone away.