Brian (Tankless) Wood.

That’s what this sounds like. It could be anywhere from the utlity transformer to your.

If neighbours have the same problem, it’s at the trans, if not, it’s between your own meter and breaker panel.

The clue is, that lights get brighter when you turn on a 240v appliance.

Have the power co check their end first (that’s free), then call an electrician.

Any bets it’s the neutral ;O)

It’s getting cooler folks, time to have your furnaces & boilers checked. And PLEASE get a Carbon Monoxide detector.

G’night all.