This is annoying but also normal. The magnetic fields cause some parts to vibrate. I know it sounds like BS but google it. You'll see.

As bad as that sound the solution sounds even more far fetched. You got to hit it with a mallet or hammer, a whole bunch of times, until the hum goes away.

I did it to a target alpha with the power off. And turned it back on every 10 hits. Took about 50 to make the hum lower volume that the machine.

I left it in place

The bolts holding the transformer core plates together might be loose. Try tightening those four bolts on each corner.

In my previous life I was a movie theater projection technician. One problem that would occur rarely in the rectifier that supplied voltage to the Xenon bulb (enclosed arc) was a hum. Some rectifiers included wood wedges that you could tamp down or screws that would force a plate against the windings. If windings vibrate, because they have become loose, it creates heat and friction and ultimately failure because the varnish wears off. I'd investigate putting a wood wedge in-between the windings and iron if that is at all possible. That said, this is a pinball machine not an arc bulb rectifier to watch Star Wars on the big screen.