[MMM]

Pandayanyan is right. No need to make enemies on day one.

Japanese is about SUBTLETY. It's very common for neighbors to introduce themselves when they move in. That alone should be a pretty good hint (surely they knew the aparment was empty until now.... Japanese people JUST KNOW).

Saying you are a student and get up early or something along those lines will be MORE than enough to tell them.

If that doesn't work, and it continues, next time you see them say something like "I had a friend over the other night, I hope we weren't too loud." When they say "No, we didn't hear you" they might also ask if you can hear them. "Tama ni hayaku neru toki mo aru kara..." (Sometimes I need to go to bed early, so...) will be MORE than enough to get the message across (assuming they are reasonable people). What ever you do, talk to THEM before you start calling the landlord. In Japan, conflict resolution is done VERY SUBTLEY so no one loses face.