How to stop humming noise out of my 2 main speakers when I turn tv off but leave receiver on?

You have a ground-loop. You have an amplifier in your receiver with a ground pin. It wants to represent 0.0000 volts.

You have an amplifier in your powered subwoofer. It wants to represent 0.0000 volts.

HOWEVER: because they are plugged into different wall outlets or the wires between the outlets adds some resistance - one of them is seeing "0.0013" volts while the other is seeing "0.0000" volts. This extra bit of voltage is like water trying to be level but you have a gutter an inch below some other which causes a flow.

You have to break the loop.

There are 3 ways to solve this:

* Common power strip - Try to plug both your subwoofer & AV Receiver into the same power strip. Sometimes this works, sometimes not.

* SUBWOOFER CABLE - they make special subwoofer cables where the center-pin on each end is connected to each other, but the outer shield (the part tied to 0.0000 in the receiver & subwoofer amp) is not connected at 1 end. This breaks the loop. Order on-line to save money

* ORANGE 3-2 PRONG Adapter - They make those orange adapters so you can plug a 3-prong AC power cord into a 2 prong AC outlet. Buy one and put it on the Subwoofer power cord. The subwoofer no-longer has a path to power ground and this breaks the loop. This is not the safest thing in the world, but do not ever, EVER open the back of the sub woofer and play around with the electronics while it is plugged in.

Hope this helps.

It's extremely simple. Just switch to a different input on your receiver when you turn off the TV. Ground loop or not, you will get no hum that way.

Humming is normally the result of a insufficiently grounded device somewhere in the component chain. Some device is most likely improperly grounded or connected.. Yeah, fix it, don't ignore it. If you want to ignore it, a couple cotton balls in the ears will work too.