...both hearing and producing the sound of the knife enables you to remain grounded in the here and now; you're aware that while you are having the memory, it remains just that and doesn't become a means of becoming re-traumatizing. Other methods that can be incorporated are imagining a safe space or image that brings you comfort or strength; speaking to yourself while tapping on your hand, etc.

The key for us as survivors who deal with PTSD is that the memories and nightmares and flashbacks lose their hold, not by going away, because they don't...but rather by the diffusing of their effect by remembering that they are only memories. That's not to minimize those symptoms, but to recall that they represent events that have already taken place and hold no real current threat over us. Your therapist should be able to provide you with some exercises and coping mechanisms, but you've already found something that works. Good for you!