Put this on YouTube a few hours ago, recorded it last Thursday (7th June 2018). I fancied taking the bus to school (I usually walk) so I just recorded it on the way up. Not the best recording ever but it does the job.
It's a constant drone irrespective of engine activity, so it's not a mechanical issue with the vehicle but rather an issue with some electrically-driven auxilliary component. My bet would be on a cooling or AC fan with a bad bearing, imbalance (missing part of one of its blades or something) or it's satisfying its hunger with some nearby bit of pipe or similar. If the fan has become unbalanced at some point, running at full pelt for days trying to keep the engine bay cool will only make it and the noise worse.