"If it's there without the light, some device in your neighbor's house
may be sending the noise back up the power line. Thermostats, fishtank
heaters, yard lights - the variety of noise sources is impressive.
Could also be loose or rusted connections on the pole/transformer."

To the above, add the photocell on the street light. depending on how
it was designed, it could make noise waiting to turn 'on', or when 'on'.
'Doc