[FFmpeg-user] Awful audio distortion with line input capture

[MrNice]

I did tests with filter
ffmpeg -f alsa -channel_layout stereo -i hw:0,0 -vn -filter_complex
volume=0.5 -b:a 320k Documents/test_`date +%Y%m%d_%H%M`.mp3
and volume=0.2
Same issue
As I explain in the first post I tried to reduce the recording volume as
well without any better sound.

Something interesting I noticed:
I start recording via CLI then I start the player: When I listen the
file, distortion appears at the very beginning
I stop the player wait few seconds and stop recording: When I listen the
file, distortion is still present half second after the end of the music.
It's look like the distortion is on an echo of the music.

Moreover:
I start record then start player. I stop record then stop player.
I wait more than 1 minute.
I start a new record (another file), don't start player, for few seconds
then stop recording.
The second file should be silence, in fact the second file has the
"echo" distorted at the very beginning, I can recognize the music, from
the end of the first file. I mean the "echo" of the previous recording
is in the next recording. Then there is silence.
Very strange.

I installed git and ffmpeg. I have a ffmpeg dir with other dir and .c
files. I'd guess I'll need to compile.
Let me know howto.