Can I leave a place where evil will most likely occur? Or do I have to wait for the evil to take place? I share my room with my brother; if I know that he will come and play a PS3 game that has music in it, can I leave the room 10 minutes before he comes so that I do not witness it?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

You can leave the place where you expect that evil (Munkar) will take place, but you are obliged to deny the evil as much as you can or leave the place when evil actually takes place; as Allah says (what means): {And it has already come down to you in the Book that when you hear the verses of Allah denied and ridiculed, do not sit with them until they enter into another conversation. Indeed, you would then be like them. Indeed Allah will gather the hypocrites and disbelievers in Hell all together.} [Quran 4:140]

It is an obligation on whomever sees evil to deny it according to his ability, pursuant to the hadeeth that was narrated by Abu Sa'eed al-Khudri, may Allah be pleased with him, in which he related that the Prophet said, “Whoever amongst you sees an evil should change it with his hand (i.e. physically); if he is unable, he should change it with his tongue (i.e. verbally); and if he is unable to do that too, then he should change it with his heart (by detesting it in his heart), and that is the weakest level of faith.” [Muslim]

In denying evil, you should take the Islamic conditions into account; among these is that it should be done in a gentle and soft manner and that it should not lead to a greater evil, in addition to other conditions that have been mentioned by the scholars.

Allah knows best.