Other things to look for, since it happens house-wide:

Neutral bonding strap in the main panel: It HAS to be there in the main breaker panel (and not loose) and should NOT be connected in any pony/satellite panels.

Also, a floating neutral can do some pretty fun stuff - when a neutral wire just isn't connected, bulbs burn brighter, there can be dangerous voltages on the neutral conductors. All fun stuff.

Good luck!
Bren R.