The Collaborative International Dictionary of English v.0.48:

Drumbeat \Drum"beat`\, n.
   The sound of a beaten drum; drum music.
   [1913 Webster]

         Whose morning drumbeat, following the sun, and keeping
         company with the hours, circles the earth with one
         continuous and unbroken strain of the martial airs of
         England.                                 --D. Webster.
   [1913 Webster]

WordNet (r) 3.0 (2006):

drumbeat
    n 1: the sound made by beating a drum [syn: rub-a-dub,
         rataplan, drumbeat]
    2: (military) the beating of a drum as a signal for lowering the
       flag at sundown
    3: a vehement and vociferous advocacy of a cause; "the
       warmongers kept up their drumbeat on Iraq"

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "drumbeat":
   barrage, beat, beating, drum, drum music, drumfire, drumming,
   flutter, palpitation, paradiddle, patter, pitapat, pitter-patter,
   pound, pounding, pulsation, rat-a-tat, rat-tat, rat-tat-tat,
   rataplan, rattattoo, roll, rub-a-dub, ruff, ruffle, spatter,
   splutter, sputter, staccato, tat-tat, tattoo, throb, throbbing,
   thrum, thumping, tom-tom