I am going to try out some of these stepper smoothers added inline from the mainboard to the stepper motors. TL-Smoother from Banggood The idea behind them is that it adds a flyback/snubber circuit of diodes that smooth the voltage signal going to the stepper motor without adding any other characteristics to the signal. It is supposed to make steppers run quieter and cooler. The end result is less jittery running steppers and better surface finish because of the smoother running. Here is a diagram purporting to show how the signal is cleaned up. The R2 doesn't really need much smoothing as it is a pretty good and sturdy design, but since you cannot replace the stepper drivers (A4988) there is a bit of noise associated with the signal and the drivers make the steppers run louder and hotter than they should. This is just an experiment and I don't expect miraculous results, at least nothing on par with the noise level achieved by TMC21xx drivers. But if it does reduce the noise some and/or reduces some heat then I will consider it a cheap win.