Ian ,
The symptoms you describe are unusual and should not be tolerated . Some simple checks will reveal where the problem is , such as having someone hold the control column firmly while another tries moving the aileron ( in the up,down and neutral positions ) Also remove the perspex cable clamp inspection cover under the wing ,to ensure the cable clamp is the correct one for that particular cable, and is firmly located . Another check would be to unbolt the spherical bearings at each end of each control cable and check for full travel ,any sloppiness or uneven resistance in the cable . Maximum 'slop' should not exceed 3 mm . Also check for control column looseness , and any movement in yoke at rear of column where the aileron cables attach . Any one ,or a combination of these faults ,will result in 'flutter' and should be rectified..... " before next flight " . At these hours I would also be checking the wing root ,and strut attachment bolts , by firmly shaking the wing to detect any movement .
Bob