Finally: Evolutionary purpose of "bedroom noises" revealed

During sex, female bonobos cry out loudly. Females in many primate species give out “copulation calls” that are typically seen as ways of showing off how successful they are at sex, perhaps to attract more mates and improve their chances of having offspring.

However, female bonobos give out these calls even when having sex with other females, whom they cannot have offspring with. Now scientists are finding that just as bonobos often copulate for reasons having nothing to do with reproduction — much as humans do — so too can these calls serve a broader social role beyond just breeding.