Can you think of two four-letter words that differ only by their first letter and mean about the same thing. Specifically, the first word means to nag or complain in an annoying way, and the second word means to continuously talk or write about something - to the point of  being very annoying.

HINT:
The second word is a homograph. Its other meaning: a musical instrument

Answer:

The words are CARP and HARP.