'Bubbling' sound when cold

Hi. The past few days its been getting cold in the mornings. When I go to school in the morning, when I rev the engine it sounds like water bubbling. Thats the best I can describe it as. Once it warms up, it seems to go away. Is this anything to be concerned about. I thought it was the heater, but it does it with the heater off too. Any help apperciated.

Swap out your rad cap with a stant or any good cap, make sure that your dexcool is not starting to gel. The new cap will allow the air to bleed out of the system. If you've never serviced your dex-crap, now would be a good time for a complete acid flush and refill (I would refill it with normal green stuff, but to each his own)....

Thanks. I've been meaning to flush it anyway...you just lit the fire under me. Just wanted to make sure it wasnt anything really important or harmful to my truck. thanks

I'm haveing the same problem with mine. I thought it was something with my plugs and wires but i'm going to try flushing my system out first. I just got finnished puting my new heater core in so i'm thinkin that might be it.