I rent an apartment with a friend. At night I can sometimes hear her breathing heavily and masturbating. Not through the room, but the walls. For some reason, sound travels easily through these walls. I noticed it when I lay in bed one night and leaned the side of my head to the wall making my ear sit right next to the wall. She is kind of shy and reserved. I of course have to masturbate as well when I hear her doing it since it's so incredibly hot.
What I've been thinking about is kind of just walking in on her with a bulging boner asking her if she needs help. That or maybe just telling her how hot it is. I don't know...
Not sure what the results are going to be though.
EDIT: I decided to walk in on her. It went okay.