Chinchilla biting but doesn't seem angry?

Hey guys - I have a male chinchilla, almost 8 months old. Recently when I've been letting him out to play he will "hump" and nibble me, which is usually only for a couple seconds and then he continues running around. Today when he was nibbling he bit down really hard. he didn't bark or anything, just bit down way harder than usual and it hurt pretty bad. Like i said, I don't think he was angry because he didn't bark? Does anyone know what this might mean? Hormones? Chinchilla puberty? lol

Thanks in advance!!