Hearing Housemate Having Sex

I live in a group house with four other people.  I live on the ground floor and there is a guy above me.  Several times I have heard a creaky bed and sex noises.  It was funny before when I was in a relationship but now I'm single and I'm uncomfortable with it.  What should I do?  Should I ignore it or say something?  He's a nice guy and we're friends but I'm uncomfortable bringing it up.