You could put insulation around it, but I wonder where the vibrations are actually coming from. The doors aren't known to close the most securely. You could try some really thin stick on foam weather stripping on the panel door itself so that it doesn't rattle. If it is the wiring inside the panel, that will be difficult since you don't want to put anything in there for a number of reasons.

Farewell - June 4, 2020