"The Hum"

That might be YOUR cause but there is lots of others. Some of it is caused by the bones in your ear actually vibrating. Nothing to do with noise in your brain
I probably should have been more specific. It's my understanding that it is the USUAL cause.

If you really want to take it farther, it's also might be due to trauma, infection, Menieres disease or a lot of other factors. But that is why I suggested that he actually see a real doctor (EMT). I seem to be the ONLY one that's suggested seeing a pro. The rest seem to be talking about aliens and other nonsense.