"~justusloonz~" wrote ...
"Richard Crowley" wrote:
I've been following a conversation over on news:rec.audio.pro
originated by a guy who is getting what appears to be CW
RFI on his microphone(s) at 9 KHz. He also reported hearing
similar "whistling" on the AM BCB.

At first I thought of those submarine communication transmiters
in the Great Lakes area (the problem is in Michigan). But, although
they run megawatts, they appear to use either higher (14-60 KHz)
or lower (40-80Hz) frequencies. And the ones in upper Michigan
and Wisconsin appear to be shut down, anyway.

http://www.fas.org/man/dod-101/navy/...cmp/part07.htm

So is there anything at 9 KHz that could be an intermittent
source of CW? Some Googling around the inter-web didn't
turn up as much as I expected.

If you are away from 60Hz lines or have few issues with strong AC
buzz, the whistling is very likely a natural phenomenon between 8 and
10 Khz. I believe it to be something related to the earth's magnetic
field and have read something about this in the past. In fact, it was
a selling point of one popular VLF receiver years ago. It was
described as almost ghostly. I bet it was a Palomar VLF receiver ad!
The device has a large loop antenna.

The whistling may be even more clear, the further you are from power
lines. I'm also curious to know if the whistling is louder and more
noticeable when the solar cycle gets cranked up again in a few years.

The OP finally discovered that the manufacturer had a
bad batch of tubes which intermittently broke into self-
oscillation in their circuit.