You to neighbor couple: "So, I heard you two getting it on last night"
Wife: "What? I wasn't home last night"
And that's how you become a home wrecker
Or you can knock on their door and ask if you can join.
You could always play dumb and pretend like you didn't know they were having sex, but say something to them about all the noise. They're bound to get the hint and realize they were being loud.
Don't tell them or they might be quieter. Then how will you spend your Friday nights?
It would either embarrass them so they'll be quieter next time, or make them do it louder because they want to flaunt that they're having sex and you're not.
My neighbors wife is quite the screamer, it is really terrible because they normally have sex in the middle of the day while all the kids are out playing on the street.
"Hey neighbor. Next time you have sex make it quieter. kthxbye"
It'd go a little something like this...