I have seen similar glitching on Spektrum car radios when the receiver batteries start to get low. I have also seen it when the transmitter was within about 1.5 feet of the receiver with the car radio.

I haven't had the issue with proximity on my DX7, just a slight buzzing coming from the servos when the transmitter gets too close to the receiver. I also found that my DX7 interferes with my 2.4ghz wireless computer network at home when I have been setting up aircraft, but no noticable interference on the radio.