Have you tried more than one FM radio? I'm sorry for the suggestion, but I have been known to miss the obvious.
Still it is possible that the ballasts need RFI filtering, for commercial you often have to order RFI filtering separate. It is an inductive capacitor circuit, I would think that you could order it after the fact. I have not ever ordered fixtures with and have never had issues. Where as I know another engineer who used to swear by them and I never saw something from him without them.
