Replacing the coil often works pretty well. But sometimes the armature plate has such a divot in it from striking the coil that it needs replacing as well.

Sometimes you can find the same coil used in the game in another, less used function, and can try just swapping the coils. At least that helps determine if on the right path.

Perhaps switch the plates as well with a less used one, if it's the same configuration...

Part of it too is how the plate hits the coil, if its uneven it will buzz. filing the top of the coil is another remedy. Also a quick fix (sometimes) is using a thin tape, scotch etc on top of the coil as a bit of a cushion. Ultimately hold coils, 1st ball coils, alternating coils will probably need to be replaced.

Ken

I use a thin piece of clear self-stick mylar from the office supply stores. I put it on the armature plate after first cleaning it off with alcohol on a cotton swab.

Many that I've taken apart have had thin washers stuck in between the coil and the housing where the screw is. I guess this moves the coil further towards the activation plate reducing the looseness causing buzz?? It does work but not sure if it's appropriate.

Rubber would add too much thickness

I found after cleaning the armature plate on an alternating relay applying a single layer of insulating tape (I think referred to in an earlier thread by MikeO) on the armature plate where it connects with the coil did the trick.

Mr. Tesla would be proud of all this buzz....

Those brass washers (and the corresponding brass screws) are supposed to be there on magnet coils that don't have the full plastic bobbin. The brass isn't magnetic, so it isolates the coil from the frame. So not really a positioning thing.