asterisk users - Nov 2008 - dial console/dsp hear crackling in headset

I am calling the console dsp and speaking just fine.
however, I am hearing crackling and all kinds of static.
I go into alsamixer and mute the MIC channel, bring the levels to zero
and nothing affects it.

Why might that be? I expected to not hear anything - especially after 
muting the channel and levels to zero.

Jerry