It sounds like us sneezing or blowing our nose.
Thumps has done it sticking his nose in dusty cobwebby places
It's easy to see the bit of cobweb or fur round his nose.
We had dusty hay during winter & he started sneezing daily even though I was tossing the hay before giving it to him. I
thought I was getting rid of the dust, but when I stuck my own nose in it Phewwww! So Isprayed it with water & messed around a bit. Now get him oats hay/farm hay. He stopped sneezing completely within 2 days when I controled the dust.
There is usually a clear discharge, later turning milky from ONE side of the nose if there's a foreign body in there.
If dust control doesn't stop the sneezing, we have to keep snuffles at the back of our minds. I'd go to a top rabbit savvy vet right at the beginning if we are suspecting that.
Good luck Hoping you'll find the dust source :wave: