I am not a chicken specialist. I've only had them for six years or seven years. First, don't hesitate to ask a veterinarian about it.
But: My chickens now and then "sneeze." No beak opened with mine, other than after running around, etc. If they are hot or excited, they pant or something like that with their beaks opened, but not when calm and relaxed and "collected."
I clean their water bowls with bleach now and then each week and keep their area clean, but I heard there was wild bird influenza around, and it CAN spread through droppings and saliva to outside domestic chickens/etc., although I don't know if it's in your area, thence a vet can help.
The bad thing is if your bird shakes its head and watery fluid dribbles from the beak. All sorts of warning signs to look for. But my birds "sneeze" that squeaky noise once a while, no more than one or two times a month between all six birds of different types. So it can be nothing, or it can be doctor time and quarantine time later if bad.
I hope I have helped. Better safe than crying.
-Birdslave
