Could be that some glue got lodged between the wing and the aileron when the hinges were glued or the torque rod epoxied.

Disconnect the servo push rods and work the ailerons gently back and forth. Take a look inside the gaps and see if there's some glue or epoxy between the surfaces. If there is, take a hobby knife (exacto or similar), and carefully clear the space between the two.

Be careful not to cut the hinges themselves. They look like thin pieces of paper between the aileron and the wing.

If you cant see anything inhibiting the aileron and can't reproduce the sound without the push-rods attached, make sure you aren't putting in too much control deflection. Double check the directions for the holes to use on the servo arms and control horns.