Every 15 to 20 years, it seems I just happen upon something going on......
When I was very young, my much older brother had brought some girl home (from a bar?). I was in an upstairs bedroom of a cape cod that only had 2 rooms, not separated by a door. The other room was not my brother's room. His bedroom was downstairs, but he may have gotten his own place at the time and my sister took it over. Because for some reason, he brought this girl upstairs to the other room.
I thought I heard a lot of licking and kissing. This went on for about a half hour or so, and then they eventually got up and left the house. Though i never said anything about it to my parents, I told my siblings what I heard. They made fun of him for it.
In my mid 20's, a couple had rented their lower level of a split level ranch to me. The place had central air, and their bedroom was directly above mine. The couple had recently split and the wife was in the house with a guy she met when i came home from work one day. The estranged husband used to call me to try and get info for his case against her in court.
He told me she liked to be tied up among other things and could potentially get loud during sex, and so he wanted to know if I had ever heard anything. Since i had more or less sided with him during their break up, I told him what I had heard that one time when I came home.
I could hear the bed springs in a fast rhythm, as the man growled at her. He either said "You lied to me !" or "You like it !", and she whined back "I know!" as she was occasionally moaning throughout. I found it hilarious, and couldn't help but laugh as I recounted it to my estranged landlord.
Most recently, about 4 or 5 years ago, I was woken up early on a warm morning with my windows open, to the squeaky sounds of my neighbor's trampoline. Daylight was barely breaking around 5 or 6 AM, and though the trampoline is up against a tall fence separating it from my yard, I of course could see over it from my upstairs window. Yes, i could see naked buttocks in the air going up & down. I believe she was on top, but I also believe they took turns.
As far as to whether or not I've ever been heard, I recall a memorable time when I was staying in a hotel in another country. I woke up in the middle of the night, super horny. I began going to work on my eventual wife, waking her as i had begun exploring her body with my hands. It quickly became an intense love making session. She was making quite a bit of noise. I could hear uneasiness in the next room. It sounded as if the person/people next door packed up and went to go ask for another room, as I heard their door close and then silence, as they had left. Given the time of the overnight, I can't think they were on their way to somewhere anyway. regardless.
When we were sexually active in ensuing years, we had a back right side upstairs bedroom, while my stepson had a front left side downstairs bedroom. Totally opposite corners, although we were right over the kitchen. One time the old bed broke & collapsed.....