Does CCr use the same Beagleboard black attached to pinball controller board? Looks like there are speaker outs on the pinball controller board. The BB doesn't have an audio port (for speakers), it sends audio to the controller board which is connected to the speakers at J6. Looks like the coindoor has volume up/down so the volume perhaps is set too low in the software. I would think everyone would have this issue with low volume since they all use the same image/version of code. Maybe people increase the coin door volume when they get the game but this will add hiss/distortion no doubt if the levels are too low to begin with. Nice that CC provides manuals (thought CCr is missing)
https://www.chicago-gaming.com/manuals/AFM_MANUAL_REV_1.5.pdf
page 104
same setup on MBr
https://www.chicago-gaming.com/manuals/MB_Manual_Rev_1.pdf
page 78