I had a problem with sneezing and runny nose bunnies too although their chests were not rattling. I was not able to cure them. Very sad.
I tried everything over the counter. I even got aeuromycin medicated feed. Tetracylin, dura, diatemacious earth ( I can't spell it and I'm too lazy to look it up), vitamins and electrolytes... Tried it all and nothing worked.
I started giving them LA 200 and tylan hoping that would help. It seemed to help a little but the problem was still there.
I even gave them their worming medicine just cause... well I was doing everything else to them.. might as well get that out of the way.
I spent hundreds (no joke) of dollars at a vet and multiple visits trying to "cure" this sneezing and slightly running nose on some of my bunnies and the vet's couldn't fix them even with medicine that they gave me that you can't buy over the counter.
I still have the bunnies but they are separated from all the other rabbits since I'm fairly certain it's contagious and I keep a bottle of alcohol for washing my hands after being near them and I also spray down their food and water bowls with hydrogen peroxide. They get plenty of sunshine ( natural bacteria killer) and good food/water.
They are perky and seem to be doing well...except for the occasional sneezing fit. I can tell because their paws are still slightly gunky from rubbing their runny noses.
They haven't lost any weight so I figure... as long as I keep them away from the other rabbits...they can still live in comfort.