Centered on approximately 17475 KHz, but audible best in USB at 17474 KHz or in LSB at 17476 is a pronounced "beep" at about 5 second intervals (edit: noted by Token to be actually 6 seconds). Noted at 1635 UTC on 7/28/2013, tipped via #wunclub on IRC, confirmed by Token to be one of the ditters. It's S7 with minor fading here.
Other frequencies active right now (these are the center freqs but I tune -1 KHz in USB):
17650 (much weaker than 17475)
17950 (much weaker than 17475)
17975 (equal to 17475)
18050 (equal to 17475)
18450 (very variable signal strength)
Other known possibly freqs are listed here:
http://www.radiohobbyist.org/blog/?p=1155Update: transmissions on all the frequencies I noted have ceased at 1650 UTC.