I've recently found that sometimes, generally in wet weather that if I use the rear demister and/or the heaters, that the EML comes on.

There's no difference in how the car drives, only thing is when I switch either of the above on, I can hear a reasonably loud clicking coming from the fuse box under the fog switches...

It's obviously not normal but it doesn't really seem to have any negative effects, and it only happens sometimes, the car is 2004 blob WRX in almost standard condition, any suggestions folks?

Thanks, Rob