Alsamixer - strange speaker noise when microphone is unmuted

[Netrick]

I found a very strange bug in Lubuntu 13.10. When I open alsamixer and unmute the microphone and increase its volume, my speakers start to constantly give some noise. When I enable microphone boost, the noise gets even louder. When I mute microphone, the noise disappers.The speaker noise happens with and without microphone plugged. Please note that this is noise from speakers and has nothing to do with recording noise. The speaker noise starts just when I boot Lubuntu and it is present all the time after, even if I'm not logged in (just sitting on the login screen after boot is enough to hear the noise which is audible all the time when Lubuntu is working).I tested it on different PCs with different soundcards - Realtek ALC 892, Audigy 1 Gold, Sound Blaster and the noise appeared on every PC.The workaround I found is installing PulseAudio and pavucontrol, then muting microphone in alsamixer and then enabling microphone in pavucontrol, after that when I use PulseAudio for audio output and input there is no noise in speakers, so PulseAudio somehow fixes it.Is it a known bug in ALSA? Maybe it's a bug in how Lubuntu uses ALSA? Maybe it's a bug in alsamixer and not ALSA? I have no idea where I should report it. I really want to get it fixed as it is very annoying in my favourite distro. And I have no clue what and where I should report.I don't want to use PulseAudio workaround as PulseAudio still has some outstanding issues in Wine in 2014 and I think the bug in ALSA should be fixed as Lubuntu is just ALSA-only distro and probably it will stay that way. And well, ALSA should be reliable with microphone input.Of course, despite the noise, sound works allright, I can listen to the music or record using the microphone etc. It's just the noise is "added" to speakers all the time when microphone is unmuted.Thanks!
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