Dc motor, h-bridge noise

Hello Electro tech online

My brother is doing a project, where he ran into problems.
The setup is quite simple and can be seen on the attached picture!
18 volt battery lead to a 5v regulator. The 5v goes to a Uc that sends signals to a finish made (bought) H-bridge that controls the dc motor. The h-bridge gets 18v, which it can easily handle.

Everything runs properly and correctly when the speed of the dc motor is slow (low duty cycle on pwm signal), also at middle speed. But at high speed, the Uc make faults. Sometimes just faults, but sometimes it also halt and it has to be reset to work again.

Can the dc motor cause noise through the shared ground? For this to happen? The dc motors are 12v but gets around 15v at max speed, can this cause ALOT noise?
How can this be prevented?

The motor has a capacitor between poles. There are placed decoupling capacitors and capacitors around the voltage regulator at correct sizes.

For us, it seems that the motor makes noise which annoy the Uc, but we have no clue what should be done, if the normal capacitors and diodes doesnt prevent this!

Thanks in advance

Place a .01 ufd capacitor from each motor pole to the frame of the motor.
Twist the wires going to the motor (about 1 twist per inch) and keep them short. Do the same with the leads to the battery.
Hope this helps.

thanks Ill do this first thing in the morning Hope it helps!