I decided to buy a six string because I've always been interested in learning to play a guitar. I decided to buy an Electra (I own an Electra Ric 4100 Clone), but when it arrived today and I hooked it up, I noticed that string six would rub up against the frets with it was strummed. This causes an audible vibrating noise. Anyone know why this would be happening? The guitar is in tune.