Frequency Generator App Helping Me

Hi
I started to hear a low frequency humming at home which I was convinced was a resonance from next door caused by a fridge or washing machine, as it seemed to ' swish'. I then heard exactly the same sound in the office when it was quiet. I have experimented with masking the noise and I use an android app. I play this through a bluetooth speaker. I find that frequencies between 55 and 80 hz work well. I also use a sounds app to play rain or water sounds alongside the frequency generator. There are also sound frequency measuring apps to check if there really is an external noise.