I had a friend who was bemoaning how his "crappy" AT&T DSL service would flake out every evening at about the same time, and he'd had techs out to replace his DSL modem twice, re-do the wiring to his house, everything! He asked me whether I was happy with TWC (I wasn't), because he was fed up and was going to switch.
We got talking in general. I asked him whether he'd also done any renovating around his house, no matter what type. He admitted that he'd recently replaced all of his exterior house lights with CFL equivalents, and I asked him whether any were on timers, sensors, etc. He admitted that there was an exterior flood light on a light sensor.
I asked him if that sensor turned on that lamp about the same time of day his DSL service flaked out. His expression dropped. He replaced that one light with an incandescent, and the problem went away.