I was redoing all my ESC's/caps and mounted 3 caps right at the esc instead of along the powerline.
Furtermore I changed to a 66/33 mix. My first test flight (mainly PH) was VERY smooth. TRD @ 6900. The "crazy going" motors do not show up anymore. I used to have the effect Mäx describes, although not that heavy because I was not holding the hexa, but it occurred in slight wind in flight.
My 2 cents are a clean motor signal and an appropriate mixing table.
Cheers
Christof