Hi Hallowed.I do sometimes listen to my music a bit too loud, but nothing crazy. I was at a music festival a month or so ago but I was never too close to the speakers and I didn't notice any ringing once I was home. I am still in education so I am not exposed to loud noises, although, there are wifi routers in each room.
I don't think it makes much difference at concerts if you are to close to the speakers or not, the music is still too loud, you mentioned going to this concert 4 weeks ago and your ear humming started 1 week after that, maybe it's connected?
What i find odd is how you experienced no ringing after a concert? I don't know if that's normal, but to my understanding anyone coming home from any concerts suffers for a few days from ear ringing.
Other then it could also very well be the cell phone tower as others mentioned.