A search turned up that the frequency is utilized by 2 different countries:
1) French AF
2) USAF/Canforce Alaska
Here is other information on the sound:
HELLSCHREIBER: FAX-like mode in that it was used to send pictures but
works more like common RTTY. The Siemans systems listed
below used start/stop signalling (FSK) and the Field HELL unit was semi-synchronous.
A couple of different machines were available:
Name | Paper width | chars per min | chars per sec | baud rate | bandwidth | tone freq
---------------+-----+-----+----+-----+------+--------------------------
Siemans GL72 | 9.5mm | 367.8 | 6.13 | 300 | 600Hz | 1000Hz
Field HELL | 15mm | 150 | 2.5 | 122.5 | 360Hz | 900Hz
Siemans HELL 80 | 15mm | 300 | 5.0 | 300 | 900Hz | 1260
I don't know if this is what you are hearing, but it fits the frequency you are hearing it on.
Take care.
