Few people can hear the horiz sweep freq.  The old 19 KHz "ultrasonic" fire alarms used to bother me when I was a kid (1960s).  I hated going into certain stores.  BTW:  You know the REAL reason the horiz output was called a flyback?  Well,  if you touched the output lead while it was turned on, you would fly back across the room! Then you would have to retrace your steps...   ;`)