Here are a couple things to try:

1. Disconnect the inputs to the speaker's amps and see if the refrigerator and lamps still make the sound. If not, then noise is coupling into your inputs. In that case, you may have a bad signal cable that you can repair or replace to fix the problem.

2. Is the computer power plugged into the same outlet as the speaker amplifier power? If not, try plugging them into the same outlet. Use a barrier strip with multiple outlets if you need more sockets. This will ensure their grounds are connected and reduce the possibility of a ground loop.