Why was West Indies pacer Michael Holding called 'Whispering Death'?

Former West Indies' fast bowler Michael Holding was nicknamed 'Whispering Death' by umpire Dickie Bird for "his smooth and silent" run-up. Bird gave the name after he could not hear Holding approach the crease before delivering a ball during a match. Holding, known for his bowling speed, took 391 wickets in his 12-year-long international career.