So then if the wiring IS good and you still get a buzz, then you should rip it all out anyway, put a new motor in it, have a certified, union card carrying electrician rewire the machine so you can use it safely ..... pardon the sarcasm, but I don't buy it.
I have several top of the line machines in great shape that will give you a buzz. The wiring is in perfect order. The motor is as well. To stop this all that's required is to rotate the plug in the wall. That does polarize the machine to match the power source.
It's the same concept as having a polarized plug wiring system that you always plug in the same way. When I get a buzz on a machine I rotate the plug in the wall and then mark the neutral side. After that I make sure to plug the machine in with the marked prong in the wide (neutral) slot of the outlet and ... no buzz.
Modern household wiring systems are polarized. That's why they use different colors in the house wiring. Red, White, Black, Green ... all go to polarize the system. That's why the wide slot in the outlets and the wide prong on the plugs, all to polarize the system. Yes, the current alternates, but it's still got a positive, and a neutral side.
I have also had many machines with bad wiring that was at fault. Gone through them carefully rewiring them as well. I've had several apart more than once trying to figure out why the buzz. When I did that I found NO shorts of any kind. No exposed wires. Nothing that would cause a short.
But, put the plug in the wall one way - get the buzz. Put the plug in the wall the other way - no buzz.
For the record, when I rewire a machine I solder all exposed wire so it cannot fray out from under the connection screws, or I use crimped and soldered on connectors. I check and double check all my connections so that there are no wires close enough to cause a short.
Inside the motors I make certain there are no wires touching the housing or any place where they should not touch.
I will also tell you this from personal experience; if you have a frayed wire, even a small one, and it touches another wire and shorts out when you plug it in, YOU'LL KNOW IT.
For those of you that are afraid of electricity, do this, then report back. When you get a buzz, have your machine checked out. If it checks out OK, put it back in the exact same place, and try again. If you still get a buzz, then flip the plug in the outlet. See what happens. I'll bet you don't get the buzz when you flip the plug.
Joe