Oh boy...
MAYBE I've discovered WHY so strange behaviours...
I was supposing that my DC motors provider got me a couple of motor with filters capacitors inside (just like the invoice said).
Instead I've found that NO CAPACITORS was inside the motors.
Now I've mounted a couple of motors with capacitors inside and still seems that anything is working...
The motors without the filter capacitors was a couple of big one that are not in the schematic I've posted, and seems that the disturbances are coming from the board that drive in PWM locked anti-phase these 2 motors.

Anyway, Steve, some good suggestion on PCB design to avoid disturbance as much is possible?
I'm using for the PWM section two LMD18201.
These 2 drivers are very close to the regulator section...
There is a ground plane on both side of the PCB connected to the logic gnd.

Thank you.