Oh no weird trumpet-like noises!

Hi Fellow Chook Keepers

I am in need of your vast experience and hope you can advise me!

Two of my hens and one pullet are making what I can only describe as trumpeting noises as they breathe in and out... I was (am) obviously concerned when I heard this so inspected the birds and there is no smell or discharge from nostrels, no puffy eyes, no wheezing or rattling coming from their lungs.  There is the odd sneeze and head shake though.  They seem fine in them selves and are eating normally (at the moment) but something's definitely up.  I just can't figure out what and wonder if it is the early stages of something respiratory or could it be gape worm... or something else...   

I have wormed them and added Respite to their water, and tried antibiotics but without any apparent effect at the moment.  It's been going on for a week and I could really do with some advice please.

I am happy to take them to the vet but to be fair she does not know much about chooks and also they are not currently 'ill'.

My chooks are exceptionally chatty...    especially my orpingtons 

But sadly the noise it isn't signing coz the noise is being made on each in and out breath... it's not a rattle or rasp... or heavy breathing!

Tis a mystery... I'll check them again tonight and keep a close eye on them over the next couple of days.