After starting up the program try unplugging the plugging the mic back in sometimes they have a static buildup that clears if you do this. Then again it could just be your mic being a bit old and beat up / bad depending on when you got it and what you paid for it.
I think that's probably your problem right there. Onboard mic's are never great. Headsets or external mics are a lot better, but you can probably make due. Definitely use headphones so you don't get feedback though. That goes for any kind of mic pretty much.
I'll be making a case for tuning down the difficulty on the trog adventures a bit. I think they're a bit steep for 2nd level; friggin' spears. Those troglodytes have no idea how to be a gracious host when adventurers come a-knockin'. I think they TPKed me four times this morning, which is a little hard for the first missions after the tutorial. One of the things the beta will do is identify bumps in the power curve.