Check the back to make sure the cord going into the supply is properly seated. My cord comes loose and does exactly what you are describing. I may replace my cord if it gets worse. I usually have to re-seat it if the cord gets bumped, its annoying.
If that does not help just replace the charger, most people including myself don't want to open one up to fix it. Not to mention I read somewhere that they have to be unplugged for some ridiculous amount of time to not have the charge to kill you!