I've had a threadless headset and a Tioga cube stem on my bike and the straight bars made a crap creaky sound. They were pretty ordinary bars so a month later i then upgraded to some Axiom risers. After a bit of riding, they too made this bloody annoying creaky sound like the bars are going to snap off at any moment. It makes the sound whenever you put a little pressure on the bars. I've tightened up the bolts on the stem enough.
It can't be the stem cause it is less than a month old and the bars are brand new also the headset is pretty new. It is definitely the bars making the sound not the cables or anything else.
Do I have to just live with this sound for the rest of my life? Is it just the design of the stem? The stem has four bolts holding the bar and four bolts holding the stem.
Try this look carefully at the gap you have on the top and bottom of the face plate of the stem. Try when you bolt it on to have equal distance between them. I really cannot think of anything else. If it persists I am at a loss.