I used to make mmm noises till I became self-aware I was over doing it.
Bringing it to her attention made her focus on it more so then it bothered her and I stopped.
Having her ramp up to motions that wont seem conducive to orgasm.
Doesn't necessarily mean she is faking it so much as she is trying to help you out possibly. I dont know which is worse. The faking it or the help.