A loop generates an electromagnetic signal, which the T-coil in a hearing aid picks up. Unfortunately the pickups in many electric guitars have very similar circuitry to a T-coil, which means they will pick up the loop signal. Also, any unbalanced cable will act as an aerial, so you should be sure to keep cable runs as short as possible, using DI boxes to convert signals from guitars and keyboards to balanced mic level, which is less susceptible to interference.

The most effective step you can take is to ensure that your loop system doesn’t cover the chancel, and any other areas that a praise band is likely to locate. If your loop is already installed, it is likely that the cable will need rerouted. This can sometimes be a tricky job, but the results are well worth it.