Chickens sneezing or so I think

Can anyone advise on the best way to treat a couple of chickens which seem to be sneezing. 

They seem to be fine in themselves and look to be eating and drinking well but seem to make this sort of sneezing sound some louder (male) and some more frequent  than others.
 
The age range is between 16 - 22 weeks.

I have 13 in total all bantams.   Not too sure if it was just 1 or 2 to begin with.  It seems to be 2 mainly with 1 or 2 of the others now and again.

No I don't give them any poultry spice.  Would it be a good idea if I did?  I have heard that Apple Cider Vinegar is good.