Articular squeaking sounds cause discomfort, frustration, and embarrassment for affected patients, especially in social contexts. Postsurgical native knee squeaking is rare, and only limited data on the subject are available in the literature. This study presents a case of knee squeaking after anterior cruciate ligament (ACL) reconstruction. A 22-year-old woman underwent reconstructive ACL surgery for an isolated tear in her right knee using an outside-in bone-patellar tendon-bone technique. Two months after the surgery, squeaking sound at knee flexion in both weight-bearing and non-weight-bearing conditions appeared without any further symptoms. The audible squeaking sound was a source of frustration and embarrassment for the patient. Given the unsuccessful attempts at diagnostic imaging, a diagnostic arthroscopy was performed during which a multistrand, long-chain, ultra-high molecular weight polyethylene suture was found moving freely in the joint. This suture, originally attached to the patellar bone portion of the graft, was removed during the arthroscopy. After the procedure, the patient reported having no more knee squeaking sound episodes. Friction of a nonabsorbable suture between the cartilage of a femoral condyle and a tibial plateau can produce a characteristic articular high-pitch squeaking sound. This should alert the surgeon to the possible presence of a freely moving fixation material in the knee. Diagnosis is clinical, as diagnostic imaging techniques have poor sensitivity.