I hope that, seven years later, they've managed to sort it out.

The worst hum I ever had to sort out was in a large, posh, hotel in a big northern seaside town. I had my power amps plugged in at one end of the ballroom and and the desk plugged in at the other end. Could I get rid of the hum!

I eventually went to the reception desk and asked if they had a house electrician. He came down, scratched his head and was similarly puzzled. This end of the ballroom is on the same phase as the other end I asked? Hmmm .... I don't think it is. Problem solved!