I myself had my first consciouss encounter with the vibrations when i went to bed one night.
The most people here mean that it gives best results if you wake up, after some hours, since then the mind is more in for the challange, not to drowsy and not to awake, but offcourse if your in for it at the starting of the night go for it. I myself never tend to feel that drowsy at the starting of night so i usually tries then.

Maybe what you heard was hypnogognic sound, when you heard your sister shut the door so violently?