My little pommie has the same problem. Like ginger899 said its "reverse sneezing". My put my thumb and fore finger on his snout and massage that area which helps him a lot. My Vet said it nothing to worry about.
This sounds very like what is called "Reverse Sneezing" . It is a bit of a mystery, as no-one knows exactly why this can occasionally happen.
It has happened to my dog about 4 or 5 times since she has been with me (7-8 years) and she is very fit and well. So it appears whatever causes this symptom doesn't threaten the dog's health.
However, I would say if she has too many 'attacks' of this, then take her to the vet to be examined, in case an allergy of some kind or nasal blockage is causing it.
Anyway, I have found that whenever my dog gets one of these Reverse sneezing attacks, I do exactly the same thing you said you do with your dog, and it does calm her quickly. The whole thing is over in about 15 seconds.
One of my dogs get sort of a 'snort snort snort' sound at the back of her throat when she get's too excited. Does it happen when she's worked up or playing or excited? Mine also sometimes makes the noise when she drinks water too fast. Does that happen with yours?
Side-Note: I think it's really quite amusing that you can't write out the name of your breed of dog without the site converting the text to "****". So if you want to write out you breed name, you have to write SH1TZU? Or what about C0CKAPOO?