1) yes, that's normal. Even if the motors stand still there is current through the coils to produce the holding torque. As the electronics is operating in halfstep-mode your motor can stop at halfstep or at fullstep. If it stops at fullstep, it is silent. Halfsteps are generated by PWM frequency. This is what makes the motors hum.
You can try by yourself. Just do one step on an axis. If it gets louder, do another step. If it gets more silent go on with the next axis. If all motors are stopped at a full step, there will be no more humming.
2) sorry, but I don't understand your question.
3) Probably there will be a mach3 guru that will answer this.
I use EstlCAM and Arduino (the italian ). For the beginning it is OK. Midterm I want to enhance my steppi with my own controller.
SC 420 mit DIY parallel + Proxxon mit Mod + SprintLayout + LibreCAD->QCAD + WinPC starter/USB->EstlCAM/Arduino + DIY Shield + DIY Vakuumtisch
2) Not shure if I understood correctly, but my machine made a strange "arrr" noise couple of times when it moved towards the end of the x or y axis at first. After performing the "Verification of the Linear Axes" procedure found in the First Steps or Getting Started document it ran smoothly.
Also if you put too much grease on the guideways it can be picked up by the rollers and get to the threaded rod. This could create grease blobs that cause some jamming.
Stepcraft 600SF (version 1) parallel port
devCad Cam Pro; devWing Cam; devFus Cam; Profili Pro 2