New RatRig v-core 3.1 high vibration at lower speeds.

Hello guys. I have a problem with newly assembled Ratrig v-core 3.1. After first calibration (flow, e-step) I tried printing regular benchy. It printed OK, but I noticed a lot of ringing on all the surfaces (ringing on corners, a lot of "noise" on straight lines). During printing that benchy tool-head was vibrating making loud noise on certain speeds (~50mm/s). Please look at pic of benchy's hull. I am using Super Slicer with all default settings. However when I increase speed (eg. +100%) all noise stops and printer produced very crisp and nice prints. I even increased speed up to +500% and it was printing very well (some ringing but that's normal at this speeds). RatRig is at work so I will post some more pictures when I get there. Can You point me in the right direction to fix the issue? Thanks guys for ALL the useful information here! BR Lukas EDIT: I noticed some minor play on X linear rail, do you think it could be the problem?