You can try to buy a power strip but the noise is definitely because of the coil squeal, technically its okay to hear some squealing noise when its on and near full power usage but you claim when its off its making that noise leads me to believe you have defective caps. Of course even though your computer is off your computer still uses electricity, this is called phantom load, your computer still needs electricity in it to respond to your touching of the power button. As a suggestion let me know if you hear the noise when you turn off the power strip itself (should have a red switch on the power strip to turn it off from where I am from).
Also this is a common issue for low end power supplies including cooler master, they are made so cheaply that they fail real easily and die out within a year or two. This does not apply if you have one of those high end cooler master power supplies. Technically from now on I suggest buying from well known brands such as Antec, Corsair, XFX, Seasonic, Pc power and cooling, Enermax, Kingwin and maybe Raidmax. Point is these brands may not be all available to you based on your geographic area. If your in North America then you will find all these brands. What all these brands have in common is that they use quality parts in the power supplies and they ACCURATELY label their power supplies and so it provides just about the same amount of watts labelled.