Hearing is Be-leafing: Students Invent Quieter Leaf Blower 

The challenge before Johns Hopkins University engineering students: Take a leaf blower, but make it quiet. Make it work as powerfully as ever, but do not allow it to emit the ear-piercing caterwaul that has gotten leaf blowers banned in some communities and cursed in many others.
Shocking their sponsors, their advisors and even themselves a little, the students did it.