Loud Buzz/Whine from motors

I have just wired up my 251's for the first time to some Anaheim Automation 34D209S-LW6 wired in series (red -A, red/white - /A, green -B, green/white -/B, black, white -- taped off). I have a Keling 36v power supply and a C10 break out board.

As soon as I power up the motors begin a loud high pitched buzz/whine. They do not get hot, the drives light up and are only warm to the touch, and the break out board is not hot and has a power light. However, when I try to jog with Mach 3 I get very slow motion, usually in only one direction, and very irregular.

I've done the driver test in Mach 3, and get a good signal. I've also tried tuning the motors in Mach 3, but changing the acceleration or velocity seemed to have only marginal effect. I have disconnected the screw drives so the motors could spin freely. They still barely move.

I've checked the wiring as best as I can and all seems to be correct. Any thoughts?