Comment # 1 on bug 955451 from Wolfgang Bauer

(In reply to Armin Mohring from comment #0)
> Steps to Reproduce:
> 1. Open volume control
> 2. Can�t reduce volume control of input to 0%
> 3.
> Actual Results:  
> Volume can�t be set to less than 16%.

I cannot reproduce this here.

Does it work if you use kmix or pavucontrol? (you might have to install them
first)

Sounds rather like a problem in PulseAudio or the ALSA driver...