Background Hum in linux (rtl_fm) but not in windows (sdr sharp)

[hhca]

Hi, ive tried this on rpi3 and a windows desktop also debian vm on the desktop. and i get a very loud annoying hum in both linux setups that is not present at all in windows sdr sharp. here is a sample:https://srv-file4.gofile.io/download/HHL2sB/20190813_00.wav
example command: rtl_fm -M fm -f xxxxxxx -l 55 -g 40 -s 12k | play -r 12k -t raw -e s -b 16 -c 1 -V1 -

 

[gofasters4]

I don't know what you are monitoring but it could be a CTCSS/PL tone. You can add a highpass filter to the play command.
SDR#'s default 'filter audio' option might be doing the same thing.

 

[hhca]

I just tried cubicSDR in windows and i do get the hum, so it seems it is processing/filter related not just win vs lin

 

[hhca]

I worked out sdr# is filtering it with the "filter audio" option. I also found out sox sinc 300-3000 gets close to this ability