RS:

That's not what tip plates do.

You might try balancing the ailerons, or getting closer to it. If you can stand the weight get some lead sticks, like that used in helicopter rotor blades, and bury it in the ailerons as close to the hinge line as you can.

And, are you sure you're getting aileron flutter? It seems to me hard to tell at 140 mph.

Surface flutter in your plane,
. often makes your crash count gain.

Bill.