Playing with the oscilloscope

This is frequency modulated signal on a oscilloscope, but the carrier frequency is lower than the modulation frequency.

In XY mode, two signals and all zoomed. Had much fun changing the frequencies and wave forms. Endlessly interesting patterns.

The special pattern you see has something to do with the oscilloscope’s internal 10kHz trigger frequency. But it’s just a guess. It could also be a ground loop problem.