Jester, I haven't read any statement regarding the actual plane other than an Alpha. Nitro has a 60 Alpha. H9 only has a 40 Alpha, however, the 40 Alpha calls out a 40 - 60 2-stroke. The OP is using an Evolution 60. I am assuming it is an H9 Alpha 40...

I doubt that this issue is a radio problem.

Most likely since it was stated their is no linkage play... There are only two reasons for excess vibration which would cause an illusion of severe crontrol surface deflection (not flutter) at WOT. However, this could lead to and result withflutter in flight.

The reasons are:

1) Out of balance Prop, balance prop.
2) Center hole was offeset during reaming, replace prop and ream with a proper reaming tool from the back side (engine side) of the prop.

I suspect one of the two is the root-cause.

Both just make it harder on a smaller airframe, when a larger displacement is used. Again, the airframe is spec'd for a 60. I would always recommend the upper spec engine. You can always throttle back and a properly balance trainer doesn't fly much different with a 60 vs a 40 on the nose. Now, decrease the wing area and using an other than flat bottom wing, it gets a bit more interesting bytrading weight for displacement. But I just don't seea significant differenceon a trainer if balanced correctly.