ax to grind vs intrusive thought

ax to grind

noun
  • A proposition or point of view to advocate, especially motivated by self-interest. 

  • A grudge or grievance, with implications of confrontation. 

intrusive thought

noun
  • an unwelcome involuntary thought, image or idea 

How often have the words ax to grind and intrusive thought occurred in a corpus of books? (source: Google Ngram Viewer )