Take a look at your cable guard. How much clearence do you have on your fletching vs. your cables? If you have room to spare adjust your cable guard inward. What could be happening is you have your cable guard adjusted out to far which can cause your string to come off your Wheel or Cam at a extreme angle. What you could be hearing is your string about to de-rail. Or I could be completely wrong but I had a similar problem two years ago with my Martin Jaguar.