Whenever I pick a note (any note, open or fretted), the note always starts off sharp, then it gradually flattens. This all happens within a couple of seconds, which makes it very hard to tune, since the note is always fluctuating. Anyone know what's happening? Has this happened to anyone?

My guitar is an ibanez s570b btw.
when you hit a string, it vibrates at a sharper frequency. hit the open string, wait for it to settle, then tune
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Quote by meow1992
when you hit a string, it vibrates at a sharper frequency. hit the open string, wait for it to settle, then tune

But as the note begins to decay, the note gradually flattens. It doesn't really stay the same for a long time. Sometimes it does though, but most of the time it's hard to tell when the note has settled. What's the cause of this?
You have to find the mid point of the note, when you strike a note, it's always going to show up as sharp, cause your slightly bending the string when you hit it, I usually keep up a picking of once every second or so when I'm tuning, it's a good mid point.
meow pretty much said it, but here's a description of why the change happens. When the string is not vibrating, it is a straight line, the shortest distance between two points. Before you release the string, it is making two sides of a triangle, and the third side is where the string used to be. The sum of the two sides is longer than the starting line: the string is stretched. When you release the string, that two-sided triangle changes into a collection of curves, one for each harmonic. Since a vibrating string is not a straight line, it is still not the shortest distance between two points, and therefore it is still stretched. Stretching increases tension in the metal, and also makes the string slightly thinner. I suspect the tension has much more effect than the insignificant change in string diameter! The energy of the vibration is absorbed by the body of the guitar, air friction and magnetic resistance, so the waves get smaller and the stretching decreases. The louder you play, the bigger the curves, the more stretch you get and the more sharpness to your initial note.