i am experiencing the high frequency when meditating. from what i have read it happens when you are in meditation. as you get close to OBE, your mental body is getting close to the 4th dimension or astral plane. As you get closer it will get louder. What this means is you basically have to raise your energy to get into the astral, so as you get closer the freqency or frequencies will get louder and higher, and become 1 tone. You experience body vibration as your energy level rises just before you separate.