Hammond XB2 drawbar noise


A just bought an used Hammond XB-2! Two drawbars (2´and 1 3/5´) introduce noise, almost like loading a game in the old ZX Spectrum computer (Hammond XB2 drawbar problem
From what I’ve had the opportunity to investigate, it looks like a motherboard issue!
Would you be so kind to let me know what you think this issue could be?
Thanks in advance!