While cleaning my strings, I felt a small node or bump on the G string. I felt the length of the string and found a couple more of these 'nodes'. Not sure if they were there all along. I am using D'Addario Helicore Pizzicato medium tension, about 8 months old. One of these nodes is big enough to cause a slight buzz when I press down on the string at just the right spot. Is this normal wear or are my strings defective? Thanks to everyone in advance.