Thank you for your query at DoctorSpring.com.
The recurrent bump you have is a sinus opening. Sinus is an abnormal tract/ comminucation. You seem to have such a sinus between your molar tooth cavity which is opening out on your gum. A sinus can form when there is an infection in the associated tooth.
You need to consult your Dentist and get an X-Ray done for the tooth with the crown. It may require a root canal treatment, if not already done.
If a already root canal treatment has already been done, it means that the tooth is re-infected and requires re-treatment or even complete extraction, if that tooth is severely infected.
Usually the sinus opening heals once tooth is treated or removed.
Feel free to ask queries.