RE: Engine noise
If you have the ignition battery near the receiver battery then you have the wires from both too near each other also. Just because it works in one situation does not make it right. Follow your radio manufacturer’s guidelines for the best performance. If you have one of the early Spectrums then this is particularly true. Here is a quote from the Futaba website. Dan.
Guidelines for setting up gasoline engine models.
All ignition equipment, including an electronic kill switch, must be mounted at least 12", and preferably 14", away from all radio equipment, including throttle servos, etc. Ignition kill switch should always be on opposite side of fuselage from radio kill switch. All pushrods going to anything related to the engine must be non-conductive (just nonmetal clevises is not sufficient).