The rattle coming from your tennis racket may be loose graphite that didn't get cleaned off when the grommets were being punched in. Take a look at this tutorial and learn how to rid your tennis racket of that rattling noise. Don't confuse the vibration sound of your strings as a rattle in your racket. If you can hear the sound only on impact, it may be the strings. Try adding a vibration dampener first.
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