RE: metal to metal contact causing interference question
The problem is created by sparking from intermittent metal-to-metal contact, particularly intermittent contact of dissimilar metals (brass & steel, for example). The engine vibration will make loose-fitting parts like clevises vibrate, causing sparking -- & producing weak broad-band radio interference. It is real & it is unpredictable, but under particular circumstances it can kill your model. It is most dangerous if the vibrating parts are in proximity to the antenna.
Engine components are normally tight fitting and insulated by a lubricant film -- no sparking. However, a muffler that is vibrating loose can also cause the same problem, although the muffler is not normally located near the antenna.