Why does my string rattle?
If the individual winding layers of a string lose contact with each other or with the core, the string can begin to rattle. However, this is a normal sign of wear and the natural ageing process of a string. The string must be replaced. Static noises that sound like rattling or clattering can also occur if the the nut is too wide. You should have the nut readjusted by a luthier.