When I first set up my darkroom this issue popped up. I was on the same circuit as my home office in a converted closet. I unloaded the circuit of other things and that helped, still and yet when the laundry is in process or the dishwasher, I still get it.
The other issue I get is related to how well the enlarger is warmed up. I've got a Beseler PM2L meter and adjust my exposure for each print with it. I can actually watch the exposure needle swing as the bulb warms up.