I'm not a pro at giant pythons so I can't talk about the enclosure issues, but...
I once bought 8yo russian rat snake female, she was calm and not aggressive at all, but very, VERY hissy. We soon realized that that was her way of telling us to "go to hell and leave me alone", but since she wasn't striking or anything we just kept handling her. After half year she was as calm as our other snakes and not a single hiss since then, so don't worry

Some snakes are just vocal too, one of ours will puff and huff if we don't let him where he wants to go. Since yours is not aggressive too I wouldn't worry too much.