Interesting. My 2005 3.6 has a sound under the dash as well, but I would not describe my noise a gargling.
Mine is more of a faint sound of actuators or relays or something or air valves changing state.
It has only been doing this for a few months. I get no codes, everything still works 100% normal. I have tried messing with my A/C controls, radio controls, seat heat controls, seat controls, windows, etc. to determine what circuit this noise is part of, no luck. It's not very loud, the radio at low levels will drown it out, so will road noise. I'm guessing that something is not right, because it hasn't always done this. Even though everything is working OK at this moment, I bet something is getting ready to happen.
HELLO, MY 2006 CADILLAC CTS IS ALSO MAKING A SOUND IN THE DASH. I CANT FIGURE OUT WHAT IT IS. IT SEEMS TO BE DOING ALL THE TIME NOW WHEN THE CAR IS ON. I AM THINKING OF SELLING MY CAR MAYBE. BUT NOW I KNOW ANYONE WHO LOOKS AT IT WILL WANT TO KNOW WHAT THAT IS & PROBABLY NOT WANT TO BUY IT. EVEN IF I DONT SELL IT, I WANT TO FIX WHAT EVER IS GOING ON BEFORE IT DOES MORE DAMAGE? IT SOUNDS COMPUTERIZED ALMOST. LIKE SOMETHING CLICKING AND MALFUNCTIONING..ITS NOT 'REALLY' LOUD..BUT NOTICEABLE FOR SURE. I WAS WONDERING, DID YOU EVER FIGURE OUT WHAT THAT SOUND WAS IN YOUR CAR?? HELP WOULD BE VERY APPRECIATED. THANKS, RACHEL