new sub makes my surronds hum

just bought a new powered sub for my home theatre i am using a yamaha receiver, mirage speakers all around with the effect off no hum,surrond on i have a hum in the rear speakers only, i am using the monster sub woofer cables tried one of my tara labs same thing sent the sub back they said alls fine,this sub has a ground plug i have heard something about grounded plugs?????? help
Humn is a common symptom with home theater systems, usually cuased by multiple grounds. The first thing to try is to "cheat" the ground on the sub. Get a three-prong to two-prong ac power plug adapter, which is commonly available at any hardware store of Rat Shacks. If that eliminates the humn, great. if not, it may be the Cable TV feed that is causing the problem. In that case, you have to find a "dc-blocker" or "ground isolater", which is a little device that connects in line with your cable feed. If neither of these solve the problem, then we are in trouble. Lastly, the reason the humn is coming from the surrounds is because of the Dolby processing, which is assuming that the humn is part of the rear channel. (the rear channel is decoded as the left minus the right main channels, thus any random noise will decoded at rear channel info). GOOD LUCK.
a typical house has 208 single phase power. what this is is two 120 volt circuits that are out of phase with each other. if the sub woofer is pluged into the other circuit " different from your preamp/amp" it will cause a 60 cycle hum. try mooving your sub woofer next to your preamp/amp and using the same power plug ( wall outlet )to power the sub woofer. if the hum goes away, find a different outlet on the same circuit of the power panel or use a large # 14 or #12 guage extension cord and place your sub woofer where you had it.