One leg of your 240v main panel could have more inductive loads, like fridges or any unit that has an AC motor in it, causing a load imbalance. A open neutral could also cause light flickering but can be difficult to find.
I dont see as many problems with alot of the newer houses that have underground service, but some of the older houses that have overhead power service tend to develop problems over the years, especially in windy areas. Years and weather can take its toll on connections. I have found people in the past complain about bulbs burning out to frequently and found that most of the time the cause was a loose neutral in the circuit box. I installed a tempstar rtu on an old 60s house back in 02, a couple years later the homeowner called me complaining that on a hot day after the unit shut down, it would not restart without straining itself and sometimes tripping the breaker. This was a scroll compressor. last summer, they were on the back porch one night and when the unit restarted, they saw showers of sparks coming down from the power pole out back. Turns out they had a severly loose connection up by the transformer. After that, they never had another problem with the unit trying to restart or trip the breaker. Make sure all your connections are secure, and if you have an older overhead service, it wouldnt hurt to have that checked out once in a while also.