Guys,
What you hear is probably the stop pin. I have this with several of my Emersons but it does not bother me. If you want to get rid of the sound, then there are a few possibilities:
1) Send it to EKI and explain them what you'd like them to do.
2) remove one of the scales and put something flexible (a small
piece of rubber or so) in the detent for the stop pin in the scale.
The fact that you don't hear it when the knive is either opened or closed fully, but only when it's half way, is because that's the only position in which the blade doesn't have contact with the stop pin and hence doesn't lock it up.