Ground Loop "Hum" Using BT Modulator

[jr_tech]

This is really a WAG, but I see diagonal lines in the "hum bars". Counting the lines as best I could, there are about 70 or so across the screen. 70 times 15750 (the horiz line rate) gives about 1.2 Mhz. Perhaps this is an indication of another strong signal, like a radio station contributing to this mess?
jr