That's soooooooo wierd, I was just about to post in here this very same problem... had it ever since I had the car, but today it's worse than ever.
Rear fog indicator light on the dash comes on then flickers every time i brake, or select reverse.
Thinking about it from the post above - would make sense it's worse today as it's been hammering down with rain.
Do you just recommend changing the bulbs or bulb holders? (sorry, wasn't quite sure which you meant up there
)