It does sound like the noise Zeus made when his eye problem had spread to his nose. It sounds most bizarre under our echoy stairs but what you describe is how I think of the sound of a rabbit sneeze.
Zeus used to do it about five or six times then stop. Like he was trying to honk up phlem through his nose.
I never saw any discharge but when the vet took a look Zeus did it and there was some discharge (thick gloopy white) - he must have been cleaning it away so fast I didn't see it.
If he only does it rarely I would imagine he has got something up his nose like a bit of grass or hay or there is a smell that is irritating him such as air freshener/after shave or something but I would get him checked out next time you are at the vets. If he starts to do it more regularily I would get him to a vets quickly as it could be snuffles.
Caz