There is a little binding of the aileron hinges going on. This is putting pressure on the aileron servo, not allowing it to find what it feels is center. It's also a good idea to apply full aileron or other control surface to see if binding is occuring then. I agree with Minnflyer and since we generally don't fly with full control surface deflection applied. binding at the extremes here is maybe not a big deal either. Still (for me personally) I will try to eliminate as much binding as possible.