If you move the cables/mic/mixer to a different location of the room, you'll lose the frequency. When you go to record stuff, you have to "sweeten" the room, and check for these things. Sometimes you'll hear just high frequency noise, and sometime's you'll pick up a CB, AM or FM frequency. I worked at a post-sound house and they used to call me "ears" because women can hear higher frequencies than men, and I was very helpful when they wanted to check their room for "noise". Sometimes moving a cable or mic an inch or two will make the difference.

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"WEMF is...." and I can't remember the rest because I didn't write it down.
- Blackness at WEMF 2007