Odd issue with fog lights

I am experiencing a strange issue with my factory fog lights - which are 100% stock by the way.
Every so often they will flicker off and on for just a split second. It doesn't seem to coincide with bumps in the road or anything like that.
Where should I start looking? The switch? A bad relay? Or somewhere in the wiring harness?
The headlights are not affected in any way.