must be getting too big as I couldnt see the microswitch and couldnt seem to get my head under the dash to take a better look... eithway, I was reading a somewhat related article which talked about the abs (or dcs) sensors on the rear wheels. I've given them a clean and problem is now gone. not sure how it all links together but seems to have done the trick. will leave it a few days before giving it the complete all clear but looks good so far.