From what you described, I saw something similar. However this "noise" 
seemed to peak here (Evansville,IN) around 13:30 UTC yesterday and  the 
FFT showed a distinct (maximum) peak at 5.192 Hz/period of 5.192 sec. 
Like you say, my instruments(two Lehmans & AS-1) have seemed unusually 
quiet for about a week. I attributed my "noise" to reaching shore of Gustav
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