My bun makes funny noises when she’s been running around, I think they are just happy noises.  From what I can tell with mine at least its usually when she is really close to me.

sometimes when my little bun is scared, he sounds like he’s breathing hard. but then he randomly makes that breathing noise for a second when i’m simply petting his head and i’m close enough to hear it… so i’m not sure what it means! just as long as he’s not distressed. he never makes this noise when he runs around though.

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.

Well, I guess I should clarify that though for some bunnies it’s normal, (There’s a bunny at the rabbit rescue named "oinky" just for that reason, however it  can also  mean they are fighting a resipitory infection – but if this noise is something he’s always had, then more than likely it’s just the way he’s made.  But if it gets worse, or you see other symptoms that accompany it like wet nose, goopy eyes, then you will, of course, want to have a vet check.