I've been hearing a curious noise on 40 (and 17) meters at my home in Northern California near Sacramento. The noise seems pretty much the same regardless where on the band I'm listening. I first thought it was something local until I heard someone else make passing reference to it. I started by noting when it was heard. I then set up to record the audio off my receiver. The noise appears once and then is over until the next time. The links to the .wav files are within the table. The files were recorded in LSB (USB on 17) with a bandwidth of 3.6k in and outside the amateur band.

Looking at the individual 'chirps' it appears that they consist of two parts, .04 seconds in duration each, separated by .015 seconds of silence.

I have also heard single bursts that one would ignore if not actively listening for them. At this point I haven't bothered to record them (except #7) because they seem to come at random, at least at this point. If you have theories or have heard the same thing on this or other bands please send information to steven AT k6bz DOT net.

15-Feb-05 I haven't heard it on 40 for quite a while now. I hear it on 17 occasionally, but not as often as I did on 40.

Here's something new,

this noise was about 10Khz wide and went on for several minutes. One of the recordings has three 'beeps' embedded. Heard on and around 18.0520 on Dec.05-04 about 2010z

New 18Mhz 1

New 18Mhz 2

New 18Mhz 3

New 18Mhz 4
This is a good one. It started out with three beeps as in recording #1. I started recording about two seconds into the sequence. As you can hear the pulses frequency increased as time passed.
Frequency Time UTC Date Sound Link
 7.2400  2110  11-05-04  
 7.0290  1609  11-07-04  
 7.2945  1700  11-11-04  
 7.2945  1703  11-11-04  
 7.2972  1903  11-11-04  recorded #1
 7.0430  1651  11-12-04  
 7.0430  1700  11-12-04  partially recorded #2
 7.2685  2041  11-12-04  five minutes after single burst at 2236
 7.2899  2258  11-12-04  recorded #3
 7.0353  1700  11-13-04  recorded #4
and 7.2849
 1655  11-14-04  recorded #5
It sounds like there are three 'chirps' sent at 5 seconds and at 19 seconds near noise level (you may need great speakers to hear). The rest comes at about 60 seconds.
and 7.2849
  1708   11-14-04   recorded #6
Exact same settings as above but with much different sound quality.
  7.0509   1838   11-14-04  
  7.2940   0043   11-17-04   Heard by two other listeners on a net. They were about 80 miles and 450 miles from me.
  7.4940   1815   11-17-04   recorded #7
Recorded two 'chirps' first at about .6 sec into the file, the second just slightly over 60 seconds later. This file is a sample of the last 'chirp' played three times then slowed by a factor of 50% for several generations to show the digital nature of the signal.
  7.3089   2028   11-17-04  
 6.9945   1530   11-19-04   recorded #8
 7.2940   0259   11-20-04  Smack dab in the middle of a net and no comments.
 7.0622   1530 - 1535   11-23-04  recorded #12
Five minutes earlier I heard this single chirp @ 1530. Same settings on both recordings.
  7.0045   2352   11-23-04  
  7.3090   1824   11-24-04  
  7.3090   1840   11-24-04   recorded #14
Seven minutes earlier I heard this single chirp @ 1833. Same settings on both recordings.
  18.127   1537   11-26-04   I thought I have have heard this outside 40 meters, but today is the first time I noted exact circumstances.
 18.0370   1627   11-27-04   recorded #15
 7.0150   1614   12-09-04   recorded #16
 18.1629   2337   01-16-05  I thought I had heard a couple of single chirps while checking out the 40m swap net today. The is the first time in a while that I've heard the entire set. I had the radio on listening to static while writing an email.
 18.1385   1705   02-08-05   First one in the last couple of weeks.

Operator: We Get Signal.
Captain: What!
Operator: Main screen turn on.