I want to be able to do that too, like this one for instance
PURE 0.33 Hz EPSILON BINAURAL BEATS | Epsilon Waves | Reality Shifting ⚡️
It would be great to be able to produce any arbitrary Hz pure tone or whatever that example is
Like 0.165Hz or anything
Are you perhaps hearing a 50/60hz signal from your electrical grid? If its higher, could possibly be frequency from your processor (or some other internal device) clock?
Those frequencies are well outside the usual working range of most amps and speakers, so its not surprising they dont work very well.
Clock speed of some kind of internal component perhaps, would be interesting if I had a way to measure it.
https://play.google.com/store/apps/details?id=org.intoorbit.spectrum
Might depend on your phones microphone quality