I had this problem as well. The axis moved smooth but still made random strange noises. After seeing Ryan’s solution to turn Z-axis acceleration from 55 to 45, I looked into my configuration. It was still on 100. Moved it down to 45, no issues anymore.
Where is the acceleration and voltage set at!
Acceleration is in the controller (marlin or grbl). For marlin, you can use the screen to set it, I think, and for grbl, you use the $ commands.
The voltage is set on the driver itself with a screwdriver. If you got the kit from v1engineering.com, then he already set it for you. Careful you don’t just to changing that value without a voltmeter, you can toast the motors with too high of a setting. Some info, although the limits they use in this video are quite high vs. experimentally sound values vicious1 uses:
Im having this issue. Ive been trying all day to resolve it by varying the stepper voltage (however I knew Ryan had it set correctly when he shipped them).
Movements with manual control work fine. I want to be sure i’m changing the right values on config.h Are the ones Ive poiinted to the correct ones to lower to 8.5 / 45 ?
Thanks
Why not use my firmware?
For whatever reason if you don’t want to use my pre-edited one you can open it and see every change I made they are all commented with “MPCNC”.
I thought I was, but right after the build / setup I could not get anything to move and the LCD was just white boxes. So, I downloaded the B16_32-LCD-112515 and the LCD came to life and the steppers moved.
I now see your build with changes
I’m learning. Maybe the hard way but learning non the less. I’ll load up your firmware tomorrow and give it a test.
Thanks.
You should be using the RC8 now.
UPDATE
Ryan, I tried installing the RC8 build and running the Z Torture test and it wouldn’t work. It tried to start but stoped right after the start. I then installed the older RC7 and it worked GREAT. I was able to do the hour long engraving (that I tried SO hard to do yesterday) without any issues. Worked Great 
Thanks for your time
That’s just it, the torture test was purposely too fast on the z axis. So it fails. If you change the speed to the firmware max it works perfectly. I have two MPCNC’s running the rc8 to 3d print since the RC8 release. They work perfectly. It is something with how estlcam is writing it’s code. I have tried turning off all kinds off things in rc8 and I doesn’t fix it, so I updated to rc8 bug fix still nothing. The laser works way better on RC8 because of the LCD fix.
I am actually not sure if it is estlcam or marlin doing the wrong thing. I am thinking it is something with ESTLCAM. I am digging in now. I even tried an older estlcam and the new experimental. Same result. If the laser works and the 3d printer slicers work it has to be ESTLCAM, right?
I took the RC8 link down, but every one that I have shipped kits to flashed with RC8 is going to be pissed. if it is a firmware thing.
I’m dealing with this problem on my new build. I can use the LCD control to move the z-axis up and down without issue, but using a file off of the SD card leads to grinding noises, hesitation and just strange z-axis behavior. I’ve started troubleshooting adjusting voltage on the driver. I’m using the 1.1 firmware offered from the main page for the 5/16 rod.
I think I’d like to try 1/16th stepping. is that a firmware change or a jumper change? I have the firmware modified to use a laser and that works great with the X and Y axis.
What speeds are you trying to use for your z axis in the gcode? That was a major issue for most people.
We had to fix both ESTLCAM and the Fusion post processor, you need to keep it under 8.4mm/s. It is not a step rate deal, it is an rpm issue.
I have the screen set to 4mm/s (if I remember correctly), that is why I assume your gcode is set to fast.
I adjusted Vmax Z from 8 to 4 using the LCD controls and it’s made a world of difference. Looks like that problem is resolved. Now I can start testing using a router.
Thanks for speedy help!
Using the LCD? You should look through the link I posted and make sure you z rapids are correct, then you never have to worry.
I definitely have more things to do. It’s all a big learning process for me right now. The quick change at least showed me that my HW is OK.
I’m also tinkering with a CNC 3.0 shield using GRBL. There really is a lot to learn, but it’s fun stuff.
I have one of those but never ended up with a Uno so I have not tried it out. Let us know what you think of it.