DC motor causing noise on the power line
Solder a 100nf capacitor as close to the motor brushes as you can, and if the motor has a metal case, also 100nf from each brush to the case. Similar to what is shown at the bottom of this page on the Pi2Go build instructions. Keep the capacitor leads as short as possible, even a large SMT ceramic capacitor would be a good option. This is assuming the noise is RF, interfering with the bluetooth. If its interference with an MCU, you could increase the capacitor value maybe 10x.