Sub blowing Christmas lights?

Being he didn't complain about other things blowing around the house sounds to me that a poor neutral connection in the service opening intermittently somewhere causing a voltage problem could be ruled out.One rare exception would be if that outlet is split,and running off of two separate phase legs.

If it happens when the sub shuts off,there could be a spike from it.When I unplug the walwart for my cellphone,I get a spike.In the bedroom,it even interferes with the tv by unplugging it.I checked it with my Fluke meter,and sure enough a small spike.

Also beside the sub turning off/on doing it,there could be a loose connection in the outlet amplifying the problem if that is the cause.