Bluetooth Noise

I made a robot car with 2 motors.
At first I piloted it "all or nothing" from an app APP Inventor 2 and everything was fine.
I made two changes:
1- I put 12V batteries for the motors (they pulled too much on the common 9V power supply)
2-I modified the app to control the direction by "long click" (therefore more progressive).
When empty (so without the motor power supply) everything is fine, I see the "orders" passing through Bluetooth (1 for front, 2 for rear, 3 for right, 4 for left, 5 for straight and 9 for stop) .
As soon as I supply the motors, everything seems, at first, to be going well then, quickly, I see abnormal "orders" appear (-1, 288, 9676, etc.) which, overall, do not influence the working (I use a Switch() Case) but often end up blocking (I guess) Bluetooth.
I thought Bluetooth immune to interference? Is that the case?
How is it that in my first version (1 9V power supply for motors and Arduino) this was not a problem?

Jean Michel

It's strange that with 9V it works fine and with 12V you have problems, I don't think it's a noise problem, but you can try putting a 16/1000uF electrolytic capacitor and another 0.1 uF ceramic capacitor in parallel with the power supply to reduce possible noise .

The motors themselves, if they are commutator motors, can be a source of large interference and overvoltages.