Noisy in bed

My friend Caroline complains about her noisy neighbors.  They are having sex in a very expressive manner and it bothers her.  But Caroline, there is no evidence that loud sex necessarily is better.  People with such a need to show off are surely not confident in their sexuality.

Diane claims that this trend in loudness was started by Brad Pitt and Angelina Jolie during a hot hotel weekend.  Apparently the elderly couple in the room next to them insisted that they never, during 50 years of marriage, had had a reason do yell that loud.  Actors!  They always want to show off!

What interests me are the cultural variables operating here.  For example: Japanese girls are famously very loud in bed.  I always wondered how this cultural difference is maintained.  I mean, where do they learn to yell like that and how is the knowledge transmitted from generation to generation?  Are their mothers teaching them or are they all watching the same porn movies?  There should be more research on this topic.