I had a similar issue with voltage variance in my house. It turned out that my old FPE panel had a stripped screw on one breaker leg of the box.
I was having random trips of certain breakers *mostly* on one side of the panel, and could occasionally feel heat on that side as well.
I knew something was wrong, but could not find it until in the middle of the night I went to the panel and heard a slight sizzling sound. I pulled the covers, and could see some small arcing.
The whole panel has been replaced ($$yeowchie!), and no more sizzling or oddball breaker trips. Much cleaner power, too.
I’ll bet that cost a pretty penny- Yeah, i don’t feel any heat- and cant hear anything- we turn the washing machine on and stand by the panel (You can see the cellar lights flickering the whole time)- but nothing seems wonky at the panel- the electricians checked the panel- I’ve gone aroudn to the outlets too to feel for heat (We once had an old air conditioner that the chiord heated up pretty bad- luckily we found it fairly quickly-) but haven’t’ found anything- The one i woudl suspect woudl be the ceramic heater- but it’s fine-