WiFi and portable phones will also cause your servos to go nuts.

Basically the RX is looking for whatever signal it can find that seems to have clock pulses on it of a pre-determined frequency.

It locks onto the strongest signal available.

If your TX level is fairly low, the RX will pick up other transmitters that have pulsing close to what it is expecting.

WiFi and portable phones often do!

If I have my planes in my house on certain frequencies, and I shut off my TX, my planes go NUTS.

A range check is always a good idea when you are away from all of this noise.