I have just cured this problem on my wifes' three door Micra.
Remove the wiper blades and then remove the plastic cover at the bottom of the screen,(these are just popout clips, no screws). The screen sits on two locating clips about one foot in from each edge. you will find that the passenger side clip is leaking water which is directly above the air fan intake and runs over the fan housing and drips onto the carpet. Use a black silicon sealent and completely cover both of these clips ensuring that you get the sealent under the clip between it and the screen. Also ensure that you seal around the popout gromets on the bulkhead. Reassemble, dry out your carpet,(I used base layer of kitchen roll and several sheets of newspaper with a weight applied to add pressure), and I am fairly certain that your problem will be solved. I feel sure that the Nissan Micra designer did not realise that the screen positioning gromet was directly over the fan intake and could present exactly this problem. (Good luck).
keith byers
August 2007