Chevy Silverado gurgling noise heard in cab while sitting at stop light

Fixed it. It was air in the cooling system. Turns out this truck doesn't have a rad cap so don't waste your time taking the 47 push pins out of the work bench. I read that you can burp it by taking the top hose off and adding coolant there but as I loosen the clamp, coolant starts pouring out so there was no point for me to try that cause I would loose everything I put in when putting hose back on. So decided to burp it via the reservoir by parking it on a hill but not front to back rather side to side due to the fact the reservoir is on the left side. apparently that worked. no gurgling the whole hour drive to work this morning. Thanks

Not fixed. Literally the noise was right back as soon as I left to go home that night. I've been paying more attention to it and now I notice it only does this when the blower is on. Doesn't matter if blowing heat or ac it will make the gurgling in the dash noise constantly. as soon as I turn the HVAC system off it stops instantly, yet comes right back when I turn it back on. I checked around the floor its completely dry, I've looked for leaks, nothing, My coolant level has never changed. Any ideas?