What EXACTLY do you mean by flutter?

If you mean that a specific control surface is "FLUTTERING", then you have a problem with that control surface. It would have little to do with weight.

A control surface will flutter for several reasons. It could be as simple as on the downline, you are going WAY TOO FAST. Typically though, flutter is caused from a bad hinge gap or sloppy linkage. The gap between the the two surfaces should be minimized and sealed. Linkage should be snug and maintained that way. It doesn't take much slop to create a problem. Could be a sloppy servo also.

Check all of these things and and report back...let us know what you find.