A lot of factors determine whether there is interference. Generally FM has less by its very nature. (You don't hear as much interference on an fm radio during a thunderstorm as you do am!). However, power of the transmitter, local radio interference, etc can contribute. Your old fm may be low power, or may not be working correctly and so it is jittery. We have 4 rc cars, run them all on am and don't have any problems. However, we live in a small midwestern town. If I were a rich man I would switch to FM.