Rewired a 1962 panel today and it hummed back at me

Customer wanted to rip out an old switchboard, said it was 'past its life.' I talked them into letting me re-terminate instead. Took five hours, and when I flipped the main breaker the hum was steady — not the angry buzz of a loose neutral, just a clean 60-cycle purr. Felt like shaking hands with the electrician who installed it sixty years ago and telling him someone still cares.