I recently bought a new Korg DTR-1000 rack tuner. When tuning, the green "in tune" LED never locks in on the note. When I first hit a note, say the open G string, the LED typically indicates sharp, then as the note sustains and falls off, the LED goes green, then eventually shows flat. Hit the string hard, it shows sharp. Hit the string lightly, it indicates flat. In other words, the LED indicator changes as the string volume changes. Is this common with the DTR tuners, or could I have a problem with my tuner?