Each time I accelerate or rev up in neutral, I would hear a very noticeable sound near the glove compartment. The sound is like water gushing through a water drain pipe...could this be something to do with the heater? I don't see any leaking fluids / coolants. Thanks for your help.

 

you either:
-have a coolant leak
-need to fill your coolant to fill level

 

I agree, your engine is low on coolant, hence air is trapped in the engine which will make that noise and can overheating of the cylinder heads as well.
Need to have someone do a pressure test on the coolant system to find the leak and fix it. Could be head gaskets or some external leak.
Mike

 

Thank you both.

 

Make sure you find where the coolant is leaking from, and use only the orange DexCool coolant.

Mike