Either it's white noise or sound outside of the human hearing range, but not physical perception, I'd guess.
Either way, there are two obvious (to me) options. One is to engineer a power cut, so hopefully that might shut down whatever is controlling the noise generation. Worth a go - presumably a quiet word with, and bottle of wine to, the building janitor might make that happen.
If that fails, you need an environmental noise monitor: the sort of thing somebody might use to put together a case about aircraft noise! I'd suggest something like the expert version of
this which you can hire for about £35/day, and will allow you to output both a recording and a noise level analysis to a laptop.
If your local council has an environmental health department, they *might* have one you can borrow, or loan at a cheap rate, for the purpose.
Your profile says you're in El Paso, in which case you could try
this company who seem to be on your doorstep and have the right equipment.
G