Ensure that your belt tensions are correct and that all of the grub-screws that hold the pulleys in place are tight.
You may be moving things too quickly. You don’t state what speed you are utilizing, but I have read that sometimes when moving too fast, it can cause a “stuttering” and/or “rattling”.
Check the Device Settings (i.e. the Wrench icon on the tool-bar). If the Fast Whitespace is enabled, disable that setting. That may smooth things out.