is it common for women to fake orgasm's? just a myth?

For some women, yes... and the reasons why can be quite interesting

Not quite the same thing (this deals with making sounds during sex, not specifically at the time of orgasm):

https://similarworlds.com/8839489-I-Am-Fascinated-By-Human-Behavior/599329-Ive-always-wondered-why-there-were-so-many-near-hy