Brushless motor back and high current and IC
Conducted ground/supply noise and radiated EMI make your signals look noisy.  

Research on this site or web to consider how to shield, suppress, filters and isolate your offending motor noise cables away from the sensitive ones or any high impedance.  

Also avoid inductive loops, with low ESR supply caps then using MOSFET Half Bridge drivers instead.  (BJT style for &lt; =15V are inefficient and outdated). 

Expect surge currents to motors are up to 10X rated current or V/DCR when changing directions or starting.

I hope the large skinny loops on your schematic will teach you these are loop antenna and your fun isn’t over until you stop broadcasting noise with BW up to 0.35/Rise time of current or voltage spikes.

Suggestions

U1 needs a low ESR e-cap directly across it and low Inductance power lines.

All Motors need a BLDC drivers with small area power loops to minimize crosstalk back to battery or PS.  The AC voltage noise may be measured with balanced twin probes in A-B mode or AC coupled to a 50 Ohm cable and 50 Ohm termination to DSO.