Salt was a snuffly bun, but I have (I think) managed to control his environment so he has no signs of it at the moment. I use the dust free hay, which they love, and wood based cat pellets in their litter trays.
He chooses never to sit in his hutch (wher ther is just a hay bedding), but either sits on top of the hutch, or on an upturned dog bed with a straw mat on it. There is a lot of air circulating around their run, and this seems to help.
Hope you get to the bottom of the sneezing.