Terror Vibrations and Subliminal Messages

I fear those sounds I can not hear… sound wave vibrations beyond the realm of human hearing, or subliminal messages slipping unnoticed into my brain and influencing my behavior.  When I was young I read a book called the Secret of Terror Castle.  An abandoned mansion in the Hollywood Hills produced a feeling of terror in all those who entered it; yet there was no obvious cause of this sensation.  By the end of the book we learn that someone is secretly playing the lowest tones of a pipe organ, sounds so low they could not be heard, although the vibrations could be felt throughout the body.  I was also quite afraid of subliminal message cassette tapes which became popular in shopping malls during the late 70s and early 80s.  These were intended to help people quit smoking or lose weight and just sounded like music.  But somewhere lurking underneath were messages that were supposedly changing listeners’ behavior.  What were those messages?  And how else were they reaching and influencing us?  I continue to be fascinated yet fearful of these mysterious “unheard” sounds.