whirr


whirr (http://definr.com/whirr)

     n : sound of something in rapid motion: "whir of a bird's
         wings"; "the whir of the propellers" [syn: whir, whirring,
          birr]
     v 1: make a soft swishing sound, as  of a motor working or wings
          flapping [syn: whizz, whiz, whir, birr, purr]
     2: make a vibrant sound, as of some birds [syn: churr]