How far is your house from the nearest pole-mounted power transformer?
My mother-in-law lives on a farm in Alberta, CA. The AC power comes for miles on overhead wires at 12KV, and is stepped down to 240V near the house. The lights dim perceptably whenever the deep-well pump starts, or when the 2.5HP compressor in the shop starts. The voltage sag is likely only a few volts, and doesn't disrupt anything, but it is a bit annoying. Smaller motors, like the hot-water heat circulating pump, the dishwasher, washing machine, refrigerator do it too, but are barely noticeable.