When the knee bends and straightens, it creaks but does not hurt, which may be caused by physiological rattling, meniscus injury and degenerative joint changes. 1. Physiological ringing: under normal circumstances, when the knee joint for bending and straightening movement, may cause the vibration of the gas in the joints, so as to send out the creaking sound, if there is no other obvious symptoms, generally do not need special treatment. 2. Meniscus injury: If the patient has meniscus injury, the creaking sound may occur when the knee is bending and straightening, then you should go to the hospital in time to improve the magnetic resonance imaging examination, and follow the doctor’s instructions for treatment. 3. Degenerative joint changes: when the patient has degenerative joint changes, it may lead to the emergence of free bodies in the joints, when the patient’s knee bends and straightens, there may be a creaking sound, and if the free bodies are small, there may not be obvious pain phenomenon. Therefore, if the patient has obvious creaking sound, it is recommended to go to the hospital for examination in order to rule out the cause of the lesion and treat the cause of the problem.