I had a noisly audio with headphones in android. But in Windows the audio is clear. Installed v4a but the problem was still there (better volume but still noisly) . Finally edited the file audio_effects.conf in vendor/etc and commented the lines:
# pre_processing {
# voice_communication {
# ns {}
# aec {}
# }
#}
Now the sound in android is without noise. But don’t know why this pre-processing was applied to all kind of content.
Hope this will be useful to someone. (and sorry for bad english)