What causes a microphone to make a waveform like this?

So at my new work I received a recording from a voice talent and his recordings were all full of clicks and whatnot. But one thing that left me confused was the way the waveform didn't circulate around 0 db? Instead it's always fluctuating around 0 db, so whenever I mute the silence between his sentences there's a pretty big chance of a click occurring.

So I was planning on giving him some feedback and would love to tell him what to do so this doesn't happen, but I'm kinda lost here... any suggestions?

read this;

http://wiki.audacityteam.org/wiki/DC_offset

yeah..looks offset..but could be this

http://www.soundonsound.com/sos/may13/articles/qanda-0513-1.htm

I've seen things like that when applying heavy effects/volume changes/compressions/etc. to audio. Would he have tried to fix/clip any of it himself?

looks like some paranormal shit... ghosts maybe?

Whenever I DC offset I throw on a HP filter or even two, that usually does the trick. I only have this issue when I'm frequency shifting like crazy though, and my offset goes insane and will destroy the signal completely, muting everything that's playing. If you have insane DC offset like that then the HP filter might not work sometimes. But it looks like you only have minor offset.

Alright, awesome! Thanks, guys. I'll look into it

it's caused by the electric signal which isn't regular, it's usually something due to super oldschool gears that have bad transformers or some bad electric installation especially a bad grounded socket, i've seen this few times,

on synth it wasn't a big problem because i made a micro fade out to grab the zero, pretty sure it will work on vocals as well but never tried