Tech question about a ringing noise

[Richard Flanders]

I think this issue is no different than running a wet finger around the rim of a wine glass. You do it just right and the glass sings/hums loudly. Same with a steel gun. Somehow when the hammer drops it does so just right and triggers the resonant frequency of the steel and it sings out. I wouldn't be surprised if the loosening and tightening of screws and putting some oil or grease here and there would change or eliminate it.