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.