Audio Systems: speaker hum, speaker wires, speaker box

Question
I have speakers in 3 rooms connected to amp, receiver, CD, turntable, TV. The
living room speakers hum pretty loudly when everything is turned off. How is
this possible and how do I stop it?

Answer
I would need to know more about the installation, wiring, how long the speaker wires runs are, the equipment and where the power lines and main panel are located, etc.

But, just guessing, you may have the speaker wires that run to the speakers that hum in parallel with a power line.

Try this:  
First, check to make sure the hum is coming from both speakers.  Place your ear right up close to the speaker box and ascertain that hum is coming out of both speakers.  This is important because often when the amp and receiver are mounted in the same room the hum is actually coming from the electronics, not the speaker.

Secondly, disconnect the speaker wires from the back of the amplifier and see if that does not stop the hum (both with the amp on and off).  Try also just one speaker at a time.

If the hum really is coming from the speaker and it drops out when the wire is pulled from the back of the amp then it indicates the speaker wires are running parallel to the speaker.  Speaker wires will have to be redirected.

But, there are many, many other possibilities.  So, take the above through the tests outlined and write back so I can get more details about your installation.

C