All 4 motors making a starnge noise

Hi everyone, new user here and I just assembled my longmill 30x30.

I have just reached the step where I wired everything up and testing if the unit is recieving power. It’s not connected to a PC as yet.

I have limit switches installed also.

The cotrol box recieved power as the red lights come on.

My questions is about the strange noise coming from the motors when the power is turned on. All 4 motors are making the strange buzzing/hissing sound almost like what broken florescent lights sound like but much louder.

Is this normal and should I continue the assembly process and connecting to a PC?

Thanks for your help.

I don’t know the answer, but I can tell you mine did not make that sound. You said it’s not connected to a computer yet, I wonder if that has something to do with it.

So I continued on and connected it to the computer. When I plugged in the usb from the longboard to the computer the motors stopped making that noise.