That shoutiness you’re feeling is called the Lombard Effect – a natural lift in volume that we get from being in loud environments. It’s very hard to control and rein in.
It sounds like you’re getting some light wear and tear on your vocal folds from being in those loud rooms. It certainly happened to me when I was in a band in uni. In your late twenties, your voice should be at its peak, instead of declining. Vocal decline happens when the cartilage begins to ossify, and that’s not until your late fifties (though this varies a lot, depending on use).
I’d recommend seeing if you can fight against the urge to get louder by singing in a very small, compact way in rehearsals. Though it’s great fun to give it your all, your voice won’t thank you for it, and you’re more likely to develop a sustainable technique by practicing in a quiet environment.