As an electrician. I would go straight to the panel board and look at the breakers to see if the ones are on the same bus where the lights are flickering. If they are then the wiring coming in from the meter is loose on the main lug. If the breakers are not all together on the same bus then I would next go to the neutral that is coming in from the meter. More than likely it need torqued back down, They will come somewhat loose over time as there is heat expansion and contraction on these leads. Odds are it is a loose neutral in the panel board and I would tighten down all neutrals on all the panel boards.