ECN Forum Forums General Topics of the Trade General Discussion Area T8 lamps swirling.....why?

I replaced some 8' T12 fixtures the other day in a restaurant with 8" T8's. All was good when I left, until the owner called the next day. The lamps are now swirling or spiraling. They have been installed now for more than a week and are still doing it. I even tried to replace some of the lamps and they still do it. Anyone have an answer for this?? Thanks, Merlin.