No technical knowledge of this, but my assumption would be that it has to do with your electrical outlet or the electrical hard-wiring of your home. I have this exact same problem with one of my external drives. I keep a mini-fridge in my office room for drinks and stuff, and whenever it cuts on my external drive will flicker off and back on.
The house I'm living in has had a lot of electrical issues, so I'm not faulting it to the appliance at all. It's probably plugged into the same outlet as the AC? Or at least at an outlet on the same in-home circuit? I'll bet if you tried in another room, it'd be just fine. Not that you want to do that.