Bob volunteered to clean up the audio at his church, and he discovered that a computer next to the amp on the desk is making the noise. But they can't move the computer. Leo says that computers shouldn't make so much noise that it would cause that much of a problem. Chances are, it's the monitor that's causing the RF interference. It's very common. It can be the power supply as well.
Ferrite bead chokes can work. He can also wrap it in aluminum foil. A well shielded case will also prevent it. Ideally, if he can move the source farther away, that would help. But using a metal barrier can prevent the interference. Fabric made of metal mesh can also solve it.