The Collaborative International Dictionary of English v.0.48:

Noiseless \Noise"less\, a.
   Making, or causing, no noise or bustle; without noise;
   silent; as, the noiseless foot of time.
   [1913 Webster]

         So noiseless would I live.               --Dryden.
   [1913 Webster] -- Noise"less*ly, adv. -- Noise"less*ness,
   n.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "noiseless":
   damped, dampened, deadened, echoless, hush, hush as death, hushed,
   inaudible, mousy, muffled, mute, muted, quiescent, quiet, silent,
   soft, soundless, still, still as death, stilly, subaudible,
   unarticulated, unhearable, unpronounced, unsounded, unuttered,
   unvocalized, unvoiced, whist