We feel that the information is very little to advice you on. We provide you the General information here. If you happen to be in the elderly age group beyond 40 years there is something called Osteoarthritis
that could happen in you which is the chronic wear and tear that is ocuring and due to it there can be the sound that you have described. Since it is an age related change there is nothing much that can be done except take Analgesics to relieve the pain, and if you find difficulty in performing your routine activities then it will need Knee replacement
Surgeries. If you are injured it could be a ligament injury
please see the doctor immediately to prevent the co morbidity in future. If you are a person involved in repetitive stress like Occupation, Athletes, Clergyman etc it could be a Stress Fracture
. Exercises and medical attention are required.