Hold your bow by the grip and pound on it up and down both sides, top to bottom with the side of your other fist....the meaty part below your pinky. Listen for rattles. Then, hold it by the bottom limbs and pound around the grip/riser area. Now repeat holding by the top limbs. Did you hear a rattle? Pay particular attention around the axles on each end. If you find a rattle identify the source and fix it.It may require putting it in a press to fix it.

If this doesn't return any rattles, I would put new whiskers on the string and cable. But if you are already looking at new and can afford the good stuff, put Winners Choice on it and then see what you think.

Most often a new twang is something loose or a loose/broken serving or actual string material itself broken under serving. It shouldn't just start twanging for no reason.