Here is a sound that i produced in audacity by generating a tone and making the frequency very low. It sounds rather like a humming of a machine or electrical appliance! good for looping and such. Enjoy !.
A 3kw electric fan heater switches on, runs for a few seconds, then gets switched off, thus demonstrating my mastery over small electrical appliances. Olympus ls-5, built-in mic capsules, no filtering.