I noticed a 63hz hum in my house that switches intermittently and randomly to 85hz and back to 63hz, holding each tone for random lengths. I can tune out one frequency, but the switching grabs my attention and makes it impossible to ignore. I've ruled out water pipes, electric grid and any local industrial processes as I hear the exact same hum at my house in Hawaii as well as at my sister's house in Texas which have completely different septic, electrical systems and I've ruled out that I'm just nuts because she hears it too and it's driving her crazy. I hear it outside as well and even when the power was out in my entire side of the island once. Any suggestions? For a short time there was a third tone that seemed to be around 40hz, but was oscillating slightly as if it were two tones together. I used a tone generator to match the frequencies to what I was hearing, like tuning a guitar by ear. 63hz/85hz. There is an 85hz tone video on youtube where someone commented they hear that in their home. Between me, my sister and the random youtube commenter, I know I'm not alone.