My 1st tube amp: transformer buzz audible 15 feet?

I recently purchased my first tube integrated amplifier from a local shop. I continue to have problems with a buzz coming from the transformer, which I can easily hear while 15 feet away. Is this normal? Do I have a defective unit?

So far, the transformer cover has been tighten by the shop, and I plugged it into a variac to bring the voltage down from the 120-122 volts coming from my outlets.

After two weeks, I find the buzz unacceptable. Any ideas?