Which one do you consider right?
(in a letter from a girl spending her holiday in Japan to her friend)
And you have to / are allowed to make a loud noise when you drink tea! (In fact, it's polite if you do!)
Actually, I would write (in this context): "...and you can make a loud noise when you drink tea! In fact, it's polite if you do!"
Please note that this is a commentary on a Western IMPRESSION of the Japanese Tea Ceremony, not what a Japanese native would consider proper, or indeed mandatory, in such circumstances.