I had a lot of interference with my MPX moviestar, twin brushless setup.
after a lot of experimenting with antenna set-ups, location of components etc (all without result),
I found that twisting the two receiver connections (from the speed controllers) together solved it completely. Now 15 minute flights without a single glitch.
The two leads were to long anyway (speedys are mounted in the wing)
So now I slide the two wing halves together, twist the leads together, and plug 'm in the receiver.
Amazing such a simple solution can make such a difference.

Maybe you can try something in that direction?