pitter-patter vs tapping

pitter-patter

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

tapping

noun
  • An act of making a light hit or strike against something. 

  • A guitar technique in which the strings are tapped against the fingerboard 

  • A connection made to some point between the end terminals of a transformer coil or other component. 

  • The process by which a resource is tapped or exploited. 

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