I've got a Yamaha acoustic which, for the most part, is fantastic. However, I've noticed that the third string's tuner seems to slip further flat -- between a quarter-tone and a semi-tone -- and more frequently than do the other five -- they seem rather stable and I generally need very small adjustments unless the weather is weird. Is there anything I can do by myself to make the one more stable? If not, it's not too big a deal as it's not like the string is coming all the way loose -- I'm just curious.