Maxx my eclectus sometimes makes a sound like some ol farmer spitting his chew out, now I have watched and most of the time nothing comes and then others it is like he is spitting. one time I reached in his cage and he spit on my hand the substance was clear and like human mucus ?
What is the possibility of it being more like a sneeze? Forget the sound and look for the source! From the nostrils or mouth?
Any sign of labored breathing and/or tail pumping?
You say sometimes, is this like once or twice a month, week, day or hour?
This time of year, as the weather here in the Great White North becomes colder an dryer, this can result in a clear mucus like substance exiting the nostrils as part of a sneeze like event, but will not sound like a sneeze in all species!
The point between a sneeze now and then and a developing problem is how often, how much, and if there are any sides of breathing problems, see by a pumping tail or a clicking sound!
Warning: If you ever hear a clicking sound and/or tail pumping, connected to they're breathing: Go Straight to your Avian Vet, call on the way to tell them that you are on your way!!!