It appears that you have located various ignition components (Ign. swtich, cutoff switch and various related cables) together with your receiver components. While the ignition box and battery are located to the front of the plane, everything switch related is intermingled with radio components. I'd move everything ignition related to the front of the plane. Also, you might try bundling your cables together a bit more as they will be less prone to pick up ignition noise that way. Keep ignition cables completely away from receiver / servo cables.

Of course there are the standard things to also check .... is your plug cap pushed fully onto the plug? This is the number one cause of interference. Is there metal to metal contact anywhere in the control system ... especially on the throttle linkage. You might check the dozens of other threads written over the last few years about this subject.

Lastly, some of those low cost (no name blue box) ignitions were prone to cause ignition noise no matter what you do. If you still have problems after you resolve known problems, you may want to suspect that and change out the ignition to the known reliable RCxcel or the same ignition sold by CH.