moan vs niggle about

moan

noun
  • a low, mournful cry of pain, sorrow or pleasure 

verb
  • To complain; to grumble. 

  • To say in a moan, or with a moaning voice. 

  • To grieve. 

  • To make a moan or similar sound. 

niggle about

How often have the words moan and niggle about occurred in a corpus of books? (source: Google Ngram Viewer )