Lately, whenever I accelerate from a stop, I hear a gurgling noise coming from the dash, like there is air/water traveling through a pipe. It's getting more and more pronounced. The engine does use a bit of coolant, but I keep the cooling system topped off. The radiator is kept full. I've been using the A/C almost constantly. Any ideas where to start on this?

 

What you hear is probably air circulating through the coolant heater passages.
The better thing to do would be to find where the coolant is going. This is allowing air to replace the coolant and when you add coolant to keep it full the air has to move around to where it doesn't make as much noise.