So which professional grade meter did you end up renting? I've been looking at a few but hearing about a model that actually caught a problem like that would be a huge help. The specs all look the same online.

Yeah, that sound is the worst. I had one last month buzzing so bad you could hear it from the driveway. I did the same thing, pulled all the breakers and went at the bus with a fiberglass pen until it was shiny. I know @ben_lewis says the grease doesn't last, and he's probably right long term, but I still use that Noalox stuff on the stabs. It at least buys you some quiet for a while. The difference when you flip the main back on is crazy, just dead silent.

Guess it was just in a really deep nap lol