Strange problem started today. I turned on coffee pot (1500W) and lights over kitchen sink dimmed slightly. Plugged the coffee pot into a different outlet in kitchen and turned it on, this time lights got slightly BRIGHTER. Went and got my voltmeter, voltage measures 130v without the coffee pot plugged in, drops to 115v and rises to 145v depending on what outlet I plug coffee pot into. Tried same experiment using a small space heater (1500w), same results. I haven't tried every outlet in the house, but I've tried this in 3 rooms and get the same result. Any thoughts what's going on, and where I should look next?