Last month me and my husband shared a rented cabin with my sister, She is 8 years younger than me and not in a committed relationship.
We went to a local pub and she ended up meeting a guy, She brought him back to the cabin and I didn't think much of it until we decided to go to bed, She asked him to stay which was awkward enough but after me and my husband crawled into bed we were kissing and making out and it became quite obvious that there is nothing to the walls but some cheap panelling which doesn't block any sound.
My husband noticed first and stopped, Looked at me then tilted his head, I whispered "What?", He said "Um...I can hear them", I listened and sure enough, I could hear my sister making weird moaning sounds, At that point it pretty much totally killed the mood for me and my husband and I laid back, All I could do was lay there and listen to my sister talk dirty (I had no idea she talked THAT dirty).
We laid there and listened to her tell him where to lick, Where to stick his fingers, his p**** and where to finish (GROSS), The whole time my husband had a b****, I'm not angry at him but WTF!!! she is my sister.
The next morning me and him were in the kitchen before she got up, He looked at me and said "So...", I stopped him and told him "If you say one word about it i'll tear your junk off and flush it down the toilet", He chuckled and walked outside.
I am not comfortable saying anything to her but I can promise we will not be sharing any cabins any time soon.