New Obsession & Cuddles: Some bunnies sort of oink/snort. Is that what you mean? Usually it's nothing to worry about unless you see your bunny suffering. But if it's just part of his normal vocalization at times, like running around, sleeping etc. Then it's just the way he was made.
Ligeia: Is it a short "huff"? Bunnies will do that as a way to warn or to show they are irritated. Jack does that all the time. He will do it sometimes right before I pet him, as if to say..."You better ONLY be petting me. Don't try to move me out of the way, or try and clip my nails, or brush my fur. Petting with hands only....HUFF!" Then he settles down once he realizes he's going to get affection.