Sounds like the lights are the problem. You could try changing the "ballasts" as they may actually be doing the RF emissions. IIRC newer fixtures have the ballast included in the lights themselves however.

Short of changing the ballast/bulbs, the only thing you can do is move the extender around to try to minimize the interference.

Well, I guess you could try building a tinfoil hat for the extender (also keeps aliens from reading it's thoughts) ;-)