I know a lot of people have the problem that after a time their G940 develops spikes or noise in one of the axes (yes that apparently is how you spell the plural form of axis), and I was unlucky enough to join the ranks.
After doing a lot of reading on the net of people attempting a lot of failed software fixes and and some successful hardware fixes I finally decided to open up my rudder pedals and take a look.
As soon as I moved the pedals the problem became apparent, the wires from the toe-brake controls move just a little bit but enough to pull on the wires which are connected to the main axis potentiometer.
This shouldn't necessarily be a problem however the terminals that connect to the pot are rather loose and move around when the pedals are moved.
So the quick fix I have done is to simply (but carefully) slightly crush/squeeze the terminals in such a way that they are a firm fit on the pot.
The more secure way which I may do in future would be to anchor the wires from the toe-brakes so they no longer move the rest of the loom, say just behind the connectors. And also for extra security maybe solder the wires directly to the pot, though at the moment that doesn't seem necessary.
I haven't had any problems with any other axes yet, but I'm hopeful that similar techniques can be applied, for those of you with such problems.