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A continuous high pitch screeching sound woke me up one morning about three months ago.

Since I work the sound control system at church, I use spectrum analyzer graphics software app (SAGS) in my tablet, which finds specific sound frequencies which spike above the average sound level frequency spectrum. They show up as spikes in the decibels and frequencies graph. If any signal sounds above a specified level, a little table at the top of the graph shows exactly the frequency that needs adjustment to bring it down. Then you lower the pot of the frequency closest to the one that spiked in the equalizer. This helps prevent those terrible feedback sounds that can ruin your nerves when using amplification systems for large groups.

The SAGS indicated that this time the frequency I was hearing was not in my head, the graph clearly showed that something was making that noise. The frequency spike was at 5.5 kHz. Later, during the day, the SAGS showed the 5.5 kHz signal gone. But I still heard the high pitch screech.

What I had not noticed at the time was that I was hearing an 11 kHz screech, whose frequency was very close to the second harmonic of the 5.5 kHz. Second harmonics are the same musical note of the original sound, only an octave higher. So after the original, 5.5 kHz signal stopped during the day, I still heard the high pitched sound, and thought it was the same sound. When I checked and found out that later in the day the 5.5 kHz was gone, I thought that maybe it was a kind of mental effect from exposure to the 5.5 kHz. The same process, every day for weeks, yielded the same results, with only slightly different frequencies spiking, all around 5.5 kHz, but nothing near 11 kHz.

My tablet’s tone generator produces a tone with the frequency you set. So you set the tone to 8 kHz and it produces a sound wave of 8 kHz. By gradually increasing the tone frequency, I compared the pitch coming out of the speaker with the one I hear, that is how I know the screech I hear has a frequency of about 11 kHz.

About two weeks ago the 5.5 signal quit for good, when a neighbor’s alarm system got adjusted. No more 5.5 kHz signal. However, I still hear the same loud high pitch 11 kHz sound, which wakes me up every morning from 4:30 AM to 5:35 AM. It is not from any external source, SAGS would have showed the spike.