Things that go Creak-a-Creak in the night

I'm a pretty light sleeper, this is a well known fact. I wake up to the cat snoring, the other licking herself, I wake up when Dave scratches his leg. Last night at 1:33 in the morning I woke up to creaking from upstairs. A very distinct rhythmic creaking. OMG... the upstairs tenant is having sex. GASP!!! I haven't heard this noise coming from another apartment since I lived on my own about 4 years ago and that girl made our rented house literally shake. Thankfully nothing fell off my walls last night, but still... what a noise to wake up to. About 20 minutes later it stopped. I felt like I was staying in some cheesy hotel, like in movies, where you can hear the person in the next room and find condoms in your bedsheets. I wonder if I should leave her a note saying "Next time you are going to get lucky, let me know so I can sleep peacefully on my couch."