What do you think about me sending my neighbors a letter about noise?
Why do you want to send a letter?
They are so loud at night with their parties until 3 a.m. in the morning. I never get any sleep.
Noise from the neighbors is really upsetting, but you have to share the community with all. You can send them a letter, otherwise it might continue. But if they ignore the letter, you should talk to other neighbors about it and complain to the landlord or HOA.
I will just yell through my window at them.
You should start with a friendly letter; if that doesn't work, an in-person visit respectfully explaining how their behavior affects you. If they blow you off, the next step is tricky. You'll have to decide to either move, or call the police and potentially have to endure months of harassments since they've demonstrated they don't care how their actions affect others.