Does it buzz in the mid-range or only when full open or closed? If in the mid-range, something may be dragging/binding. If at one end or the other, a minor mechanical adjustment may alleviate the problem. Possibly a linkage adjustment or moving the engine slightly on it's mount fore/aft. Make all adjustments small and only as much as needed. The small amount of engine movement should not effect the CG. Also be sure your batteries are fully charged.

Alpha 60 is a good trainer.

Let us know what you find