hmmm... cant say i am an expert but I have a similar problem on a 46 plane that i have called the Pepper. It is an old design, low wing, box fuse, but the sound it makes is the same as you described in the previous post.
My hinge gaps are sealed on the ailerons so it cant be that. The only think i can think of is that the material that the ailerons are made of is soft balsa and becasue they are so long and slender, they may be flexing at the tips.
It only happens at full throttle settings. At half throttle, the plane flies very sweetly.

There is not much, if any slop in the aileron linkages.

I would be checking the linkages on my ailerons; do you have any flexing on the elevators and rudder?

if i remember back to my Giles, they came supplied with terrible wire/dowel rods that had a LOT of flex in them... so much that you could easily twist the elevator halves opposite directions....

are yours the same?

cheers