Using tin foil is a well known diagnostic technique, but it is not the engineering solution. However, there is nothing wrong with trying it. I've certainly known it to work on an M10 + Battery box combination.
I have a CA9100 and it is not immune to interference, especially from stage lighting. That isn't a criticism. Managing EMC is a black art and you are at the mercy of the other device(s). Remember the definition of electricity. It's magic and it hurts if you touch it.