Fan noise in freezer of my GE side-by-side...

Question

I have this noise coming from the evaporator fan in my GE fridge model # GSR23VSTASS. It only makes this noise when the fan is in running in it's slow mode. If I tap the vent that covers the fan, the noise disappears. A few days later it comes back. There seems to be a bit of ice and frost underneath the ice-maker. The temperature of the freezer is 0 degrees and the fridge part is 37 degrees. If this is an ice problem, is there a way of preventing this?