I came across this (in context) in a book. Thought it was a freakin' awesome word.

niggle |ˈnigəl|verb [ intrans. ]cause slight but persistent annoyance, discomfort, or anxiety : a suspicionniggled at the back of her mind | [as adj. ] ( niggling) niggling aches and pains.• [ trans. ] find fault with (someone) in a petty way : colleagues say he loved to niggle and criticize people.nouna trifling complaint, dispute, or criticism.