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« on: December 28, 2012, 1954 UTC »
I hope I'm not repeating the valuable info provided previously. That said: Try actually unplugging everything, then check for the noise at each step. It's important to remember that most modern plug-in devices, most especially those with a clock, timer, or remote control are never truly off as long at they are powered. I had an electronics professor who explained to the class that he did a yearly "audit" of his own home where he would unplug everything and check the Watt-Hour meter. If it was still turning, he'd go and search for what he missed, repeating the process three and four times until it stopped turning. "You'd be surprised..." how many things we all have plugged in. He was also a ham and concerned about noise as well as his monthly bill.
To sum: you may find many noise sources in your home. My computer monitor makes all kinds of noise on HF that varies with what's on the display.
Good luck and have fun.