Translational lift
I’m not so sure that I believe that the ‘burble’ is TL. That’s just the helicopter breaking into clean air not affected by the ground. Want proof? Take a helicopter to 200ft, ie way outside ground effect. See if you get the ‘burble’ like you do on transition close to the ground……
Translational lift occurs even with slight airflow across the disc, not 12-15kts.