I have always run my futaba r700 with a 6V pack unregulated. Never any problems. One thing i do like to do is stay within brands. I use futaba receivers with futaba servos. I would suggest trying different servos, as you have eliminated the idea of the RX or TX. A guy i fly with has a funtana with saito .72 BK using a 9CAP tx and not sure of RX but he uses JR servos, 2 weeks ago he had the same problem. His servos fluttered around the neutral point and eventually would stop fluttering, but it wasn't a violent flutter, just a little "wiggle". I think his ailerons did this because they are massive and have alot of weight. He decided to fly it (maiden) and had absolutely no problem. we also noticed if he put his finger under the aileron and push-up a little, toward the center, it would stop at neutral. We figured the airflow over the surfaces helped the ailerons center in flight. He had an uneventful flight and made a smooth landing.

If you want to know, not relevant to topic but:

Personally i use the r700 RX, T6XAS TX, S3004 servos all around (changing soon), and a 46FX with slimline pitts muffler. I like this plane with the .46, many will say otherwise, but it flies at a good speed, but wont go near overspeeding in straight flight at WOT, always throttle back on decent to prevent over speed. Aerobatics a great, with a .46 on the nose it fly's like a sport plane on steroids. It waterfalls nicely, snaps great, does spins (still working to get flat spin), stall turns, whatever, just dont expect to do 3D with the 46. I run an APC 11x5 sport prop with omega 15% nitro fuel. I can just about get it to hang at full throttle, but i wasnt it expecting it to with a .46 walls and elevators are done easily, as is the heart attack (do one inverted ). It will perform just about every move with the .46, just not the stalled wing maneuvers, i have yet to try a harrier, but i dont think it will do it at too slow a speed or too great AOA.
Just thought you would like to know this stuff before you flew it, happy flying, hope your problem gets fixed, HAVED FUN!!

sean