Hi
At the moment replacing the speak is unlikely to help
Your best bet would be a fully disassemble the furby and keep a eye out for any corrosion as these furbys are extremely prone to it due to them being able to use battery’s that can leak
If any corrosion is found ,clean it away with isopropyl alcohol and once fully clean carefully clean it again with distilled water(the distilled water will neutralise anything that’s too alkaline or acidic)
After that reassemble and see if the issue persists
If you see anything you are unsure of let me know any il try my best to help with it
Hopefully this helps
Any questions please ask
Thanks:-)