Possible Clues:

• Talked nonstop on one subject
• Dwelled (on)
• Dwelled tiresomely (on)
• Went on and on
• Insisted (on)
• Was a nag
• Reiterated, with ''on''
• Talked nonstop on a subject
• Talked repeatedly and tiresomely - on musical instrument?
• Talked repeatedly and tiresomely about