Hey Ryan, aircraft are teh only things that use a clunk. On a nitro truck or car, it's bottom fed from the back since that is where the fuel is most of the time.
But that is a great point. You could have a pin hole in your line causing air to get in there. You could also have some junk clogging up your carb. Take the carb off and clean it out thoroughly. Meaning, remove the high and low needles, remove the barrel and completely clean it.