pitter-patter vs pounding

pitter-patter

noun
  • A soft, percussive sound, as of tiny feet, or of rain on a rooftop. 

pounding

noun
  • An act in which something or someone is pounded. 

adj
  • Characterized by heavy or loud throbs 

How often have the words pitter-patter and pounding occurred in a corpus of books? (source: Google Ngram Viewer )