Is the snapping painful? Did you have a previous injury around the knee or hamstring? Difficult to assess why you’re having this snapping sensation but sounds like you may have a subluxation of the biceps femoris tendon due to an abnormal insertion. This can be genetic or due to a previous injury. Snapping hamstring syndrome is not a super common phenomenon and there really isn’t a ton of research around the topic. You can try to manage symptoms with still stretching, perhaps some compression or voodoo wrapping, and modifying training or squats so as not to irritate the area. However, all of these will just work towards managing symptoms and there isn’t really any mobilization or exercise that will fix the abnormal insertion. If you have been able to train around the issue I would continue to do so but if you are having pain or the issue is limiting your function you may have to seek out a medical pro for a differential diagnosis and management.