I found that what I was doing wrong was not making my hand slide more towards the front of the neck in order to get fingers more straight on to the strings.
The way I corrected this was I place the back of the palm of my hand more towards the bottom of the neck. I've got fat fingers and found that trying to barre the chord was causing the bottom string to be muted so I had to get the three fingers there. Two wasn't getting the chord to sound right.
With the "buzzing", sounds like you are on the fret itself or not pressing the strings off there behind the fret. I too had that problem as well. Use your thumb or the fat part of the base of the thumb to PULL your fingers into the chord more. That's how I got that solved. But that's just me.
I will let the instructors correct me if I am wrong.. well they will anyways.. what I love about these fine people...

Party on Wayne and Garth!