The Collaborative International Dictionary of English v.0.48:

Thrum \Thrum\, v. t. [imp. & p. p. Thrummed; p. pr. & vb. n.
   Thrumming.]
   1. To furnish with thrums; to insert tufts in; to fringe.
      [1913 Webster]

            Are we born to thrum caps or pick straw? --Quarles.
      [1913 Webster]

   2. (Naut.) To insert short pieces of rope-yarn or spun yarn
      in; as, to thrum a piece of canvas, or a mat, thus making
      a rough or tufted surface. --Totten.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "thrumming":
   beating, birring, bombilation, bombinating, bombination, booming,
   burring, buzzing, clicking, droning, drumming, fluttering, hum,
   humming, low rumbling, palpitant, pounding, purring, spattering,
   spluttering, sputtering, staccato, throbbing, thumping, ticking,
   whirring, whizzing