Scroll down to the bit about bars. I'm not sure if there's anything in there that will help. Perhaps you could grease the wedge and its bolt. Is the sound definitely coming from the stem?
I'm all out of ideas, but there are nearly 2,000 users on here; someone will know what to do.
Here's what Sheldon has to say:
http://sheldonbrown.com/creaks.html
Scroll down to the bit about bars. I'm not sure if there's anything in there that will help. Perhaps you could grease the wedge and its bolt. Is the sound definitely coming from the stem?
I'm all out of ideas, but there are nearly 2,000 users on here; someone will know what to do.