Once I started playing with the U360, I noticed the same behavior. If I moved swiftly, everything was fine, but small slower movement produced a "rubbing" effect. It sounded bad and felt worse. I told my dad it sounded like I was chopping wood.
I went and got some white lithium grease and put it on the bearing pivot of the joystick. Put it back together and played it for a while. Then I broke it down and applied a little more grease. Since then, I've had no sticking, and the stick feels very smooth.
I'm very happy with the stick now, and even if I have to grease it every so often, it is worth it to me.