I honestly have no idea what it is man, the techs at Nissan didnt really have a clue either. We looked at and listened to 2 other Micra's and neither made the sound our cars do.
But yeah you'll be the first to hear when i get some news on this issue! Is there any chance you could get a video uploaded of your car making this noise? I want to add it to my claim so Nissan Canada see's im not the only one with this issue and its clearly something faulty with these cars.