I recently hired an energy efficiency retrofitting company to do some work on my house, which included sealing the house, replacing/sealing furnace ducts and blowing in new insulation to the attic. The insulation was done last, while we were out of town for a few days, and since returning we've noticed a periodic and very short dimming of the overhead lights in our house that was not there before. We've always had some amount of dimming when certain high draw appliances or devices turn on, which I think is fairly normal, but this is different and more frequent. Also, while I have no measurements to confirm I'd swear that it happens less or not at all after the lights have been on for a couple hours. It's entirely possible that this coincidentally just started happening after the insulation work is done, but the timing is very suspicious. Unfortunately, my knowledge of home electrical systems is limited at best, so I'm at a loss to think of what the insulation contractor could have done to cause this. Any thoughts/suggestions would be appreciated.