That's a tough one. I take it you do not work so don't get up that early in the morning and or like music/TV, etc. if you do? I live in a townhouse now and our neighbors sometimes play music loudly from outdoor speakers when they're outside; fortunately their tastes are a enough similar to ours (they are 15 or so years younger) that it is tolerable.

Does your lease have any hours on it for noise? I'm like you, inclined to not be able to think of "friendly" ways to complain so I put it off. I might be tempted to see if I could move to a 3rd floor apartment and/or I'd get headphones with my own music/talk.

Do you have a favorite type of music? Maybe give them a cheap CD of your favorite kind with a jokey message like, "If you are going to play music before 9:00 a.m. or after 10:30 p.m., please either keep it way down or play something I will enjoy too".