Well..... if I may add my two bit on the topic of Flutter.....
Well it could just not that the servos have the flutter..... if it is so... just change the servos and find out....
Assuming that your servos and control links do not have much play in the linkages.... so play will always remain but it should be as small as possible...
Flutter is basically a problem which is encountered on control surfaces because the control surface is not correctly balanced with the main wing / stabilisers. Flutter takes place on all types of control surfaces and reasons of the same can be understood one the aerodynamics if Flutter is understood. In face Flutter takes place in all structures which are subjected to Aerodynamic forces....
You may like to read the following links....
http://www.wired.com/2010/03/flutter-testing-aircraft/http://www.iitk.ac.in/infocell/Archive/dirjan1/flutter.htmlhttps://en.wikipedia.org/wiki/AeroelasticityThis link explains the issue and gives a few methods to correct it for aeromodels.....
http://www.rccr1957.com/flutter.pdfHowever in my understanding of aerodynamics.......
In aeroplanes where the manufacturer is guarding against flutter because people are involved, he spends money to do the tests and get the optimum conditions to reduce flutter....
For us aeromodellers who often make out own planes and most often then not there are a hordes of irregularities of balancing and streamlining.... we will have to live with flutter..... Just check your model for the points as stated by Sanjay Sir.... and make sure of a few things:-
1. That the control surface is not made of a heavy material.... as it will result in the CG of the elevatore or the rudder falling behind the hinge line.
2. That the hinge line is located as close to the GC of the control surface as far as possible....
BOTH THESE CONDITIONS ARE DIFFICULT TO ACHEIVE.
3. In case you can give an aerodynamic balance to the control surface you will eliminate most of the flutter... something like given in this picture....
http://img.tfd.com/mgh/av/th/f0017-01.jpg and you may like to read this....
https://en.wikipedia.org/wiki/Balanced_rudderBest wishes and Happy and Safe Flying......
by the way.... my models also show signs of flutter as I have not used most of these remidial actions on my models. All my models are self made but I do ensure that I give some balancing and that my control surfaces are very light Balsa.... Yes they still flutter...