If you remove the wiper motor (4x 10mm bolts & gently prize off the linkage) move the wiper arm back and forth.
If the noise has gone its the motor (like porkpie mentioned)
If the noise is there its probably the bits the wiper arms attach to. I've had this on a few Micras! Soak them in 3 in 1 oil, better than WD40 and work them back and forward by hand for a few minutes. That usually does the trick!