I have a main transformer in one of my welders that's just starting to buzz. I checked the bolts holding it down - tight. I pushed on the top corner, sideways, so as to compress the laminations together - bingo. Down about 1" from the top, a bead is run. I don't want to monkey with the bead.
There is a wedge pressing the laminations together, but it's been varnished along with the rest of the transformer core, and doesn't want to move.
However, the top corner of all the laminations is punched with about a 3/8" hole, and all these holes line up. I'm considering looking for a plastic tube, cutting it to length, and finding (or making) a couple of plastic top-hat washers and putting a 1/4-20 bolt through the hole and snugging the bolt up a little. I'm pretty sure that would work, since a few ounces of sideways pressure cuts the noise nearly in half, but I'm wondering if it's safe to do.
I also am wondering if I really need to worry about fully insulating the bolt, or even insulating it at all.