I would still bet it's a dirty lens, but it could also just be sensor/sensor amp problems that require the camera to be replaced. Try cleaning the lens first, if not it's probably a sensor amp issue. You can try shooting with low ISO and long shutter to check. Just make sure you use a DC powered LED, since the third possibility is that you just have poorly maintained lamps and you're just capturing the cycling.
I did a long exposure and ended up with something very messed up, I thought in only happened with the flash on and non-macro distances, but this was new.
15 sec exposure
The one that looks like modern art(blue) is the one with long exposure.
The other one is normal on auto mode with flash.