I recently was checking out this AV Rant podcast:
The male host has a speech impediment which seems to be common in “nerdy” types. (I believe Daxflame from Youtube also has it.) I was a little amused that the guy has such a stereotypical voice for an AV nerd. (He refers to himself as a nerd.) It’s most apparent on the letter D. Words like “didn’t” don’t out very clearly. Does anyone know what this type of speech impediment is called?
I could barely hear anything amiss except maybe he does say “dint” for “didn’t”. I don’t think this is an impediment, rather some regionalism that I can’t place.
I don’t hear anything significant either. I agree with Cosmic Relief; you may be hearing a regionalism you’re not used to. Many of you guys south of the border sound a lot more “different” to me than the people in that recording. 
There is certainly something funny about his “d” pronunciation. Can’t say I’ve noticed it in any other speakers before, but then again I may not have noticed it with this guy if it hadn’t been pointed out.
He sounds like he has a very mild mid-Atlantic (Philly) accent. Very mild. He also has some of what I call a “young cohort” way of speaking, noticeable in the way he pronounces a long “o” sound. Seems like most people under 30 talk that way. Phone becomes something like “Pho-oon”.
My take on this guy is that he has an eccentricity (maybe that “youth cohort” thing) where some d’s and terminal t’s (as in get) are articulated as a glottal stop, but not consistently. I also noticed a couple of Tom Brokaw-style back-of-the-throat l’s, though not consistently (such as sometimes when he says “blend”). Not sure I would call any of this an impediment since I think he is perfectly capable of a more standard pronunciation when he thinks about it.
Yes, sometimes he sounds like he is missing the “d”.
A related question - what exactly is the origin/explanation for the stereotypical geek/fanboy speech pattern, examples being the nerd on Robot Chicken and if I recall correctly, Jon Stewart also does a similar thing? To me it kind of sounds like the cheeks are sucked in a little bit and saliva is collecting in front of the airflow, combined with a higher pitch.
Jerry Lewis?