If your stick is getting on a bit, dust and debri can find its way into pots, causing spikes, etc. If your stick is really old it could mean a failing pot resistor track. You can get electronic spray cleaner that you spray into pots and it cleans them out. You will have to most likely take the base of your stick though. If this doesn't work then its time to look at a new stick.
Some people spray WD-40 into their sticks to lubricate them DO NOT DO THIS. You must use electronic cleaner spray.
I have set of CH pedals which from the factory always stuck on left rudder... I put up with it for years until one day I pulled the back off and sprayed the pot with cleaner. They have been perfect ever since
NG <S>
PS Disregard the above if your system uses hall effect sensors.