Different ringing patterns on flyback output
I have also seen the same waveforms on Multiple occassions and yes they are due to common mode noise, if you use differential probe you won't see it on Flyback outputs.
Also if you use 2 single ended probes with one at the output and one at ground and use A-B function on DSO you won't see it.
thanks for this important discussion.

Regards,

Chaitanya B