The Collaborative International Dictionary of English v.0.48:

Rataplan \Ra`ta`plan"\ (r[.a]`t[.a]`pl[aum]N"), n. [F.]
   The iterative sound of beating a drum, or of a galloping
   horse.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rataplan
    n 1: the sound made by beating a drum [syn: rub-a-dub,
         rataplan, drumbeat]