Because I can hear the um...."rhythmic activities" and the squeaking is becoming bothersome
Post it note on the door. "We can hear you."
My aunt had this problem. She could hear the guy and whatever girl for the night "going at it". She went up there and told him "if I'm not getting any I don't want to hear you getting any".
All jokes aside, do you feel comfortable enough talking to the upstairs neighbor? Is this happening every day?
Best line someone ever shared with me: a note put on the offender's door that said, "If you can't be quiet, can you at least be DONE by 11 PM?!" LOL