[Spooks] New monitors help request.

[Christopher Ayres]

Hello, I am very new to the search and monitoring of numbers station and of course new to this list.  I am presently stationed in Japan and I have been listening from here with a humble set up to get started with :

Current Location: Yokosuka, Japan
Grid: 35.14.1N 139.40.5E
Receiver: SONY ICF-SW7600GR Portable
Antenna: Kaito KA-35 Active indoor

On Saturday 16 Feb 2013 at 10:37 UTC I was checking frequencies which had been reported recieving Numbers Station transmitions on the Spy Numbers Data Base by TI in Japan on 5/3/2011.  During my search of Frequency 6445 Khz USB I noted a signal which I could not identify.  I could also recieve the same signal on 4219 and 6217 Khz but weaker.  I am attaching a sound byte.  Could anyone please tell me what this  might be? 

Thanks, Chris