Strange sound from steppers

5x DRV8825 (Vref = 1V) to NEMA 17 on Geeetech GT2560 v3.0 Marlin board with Meanwell 24V 15A DC power supply (leftover parts from Geeetech A10 3D printer - am in Ozzieland down under).
(MPCNC part 4 |

M17 to energise steppers [OK]
Faint same frequency hi-pitch sound [OK]
M18 to unpower steppers [OK]
Run crown test pattern [OK]
M17 to energise steppers [OK]
Faint rising frequency hi-pitch sound that cuts out and repeats indefinitely [not OK]

Probably time to swap PSU, stepsticks and/or logic board. Just wondering if anyone has come across similar symptoms perhaps.

Here is a sound file attached: