I've put a couple of very good links at the top of the first post. I've heard a few stations lately myself, but mostly with appalling reception. Apart from..
...for some years I've been listening to an on-off buzz, wondering what it was. This week I found out, and it turns out to be a Russian military station that has, in 20+ years, ceased the buzz only three times to give out numbers-style messages. There's even a wikipedia page about it:
UVB-76 is the callsign of a shortwave radio station that usually broadcasts on the frequency 4625 kHz (AM full carrier). It features one of the most unusual, mysterious, and widely discussed broadcast contents on the shortwave dial: a short, monotonous (E-natural) buzz tone, repeating at a rate of approximately 25 tones per minute (Sample Sound), for 23 hours and 10 minutes per day (transmitter maintenance apparently takes place between 7:00 and 7:50 GMT). One minute before the hour, the repeating tone is replaced by a continuous tone, which continues for one minute until the short repeating buzz resumes. Notably, the buzzer has ceased for a voice transmission exactly three times in the station's (20+ year)
history. Its purpose, however, remains unknown.
Here's the noise I've been listening to for years:
http://www.geocities.com/uvb76/buzzer-1.mp3!!!
And here's the details of the station:
http://www.geocities.com/uvb76/
I looked up the co-ordinates on that site and looked at Google Earth. Here's the broadcasting station:
.