We had a very affectionate bun (male) who would "hum" when excited, or when he ran over to see us....our new bun, a 3 month old rescue lionhead who we picked up on saturday, hummed at me for the first time last night.. I went to sit down near him and he came running over to see me and hummed! I was really pleased, as I've always assumed this is a happy noise. Is this correct?!