Hello Markus,
I watched this frequency in qrss10 approximately from 23z till 05.30z - absolute 
"silence".

73
Andrey RN3AGC in KO85SV

Hello LF,

since Nov 28, 11:05 I am seeing an unidentified weak signal on ~ 137.2445 kHz, 
about 1 to 2 uV/m with northerly incidence, and
some QSB indicating nonlocal origin. It's now transmitting a continuous series 
of audible dashes (1 s on, 1 s off). The frequency
is drifting slightly and does not appear to be phase coherent from dash to dash.

Any hints?

73 de Markus, DF6NM