How to avoid Coil-Whine on GPUS? Bought RM1000x & RM1000X Shift, both had coil-whine...

The PSU is rarely responsible for coil whine. It is usually a GPU design issue due to inductors or ceramic capacitors vibrating. Alternating current creates an alternating magnetic field. The solution is either damping the components to reduce vibration or adjusting the switching frequency/current to a lower amount. For example, setting an FPS limit and undervolting will usually reduce coil whine by a noticeable amount. A heavy cooler + thick thermal pads will damp the inductors.