'whirr' definitions:

Sound of something in rapid motion; "whir of a bird's wings"; "the whir of the propellers" [syn: whir, whirr, whirring, birr]

Make a soft swishing sound; "the motor whirred"; "the car engine purred" [syn: whizz, whiz, whirr, whir, birr, purr]

Make a vibrant sound, as of some birds [syn: churr, whirr]