To be direct, I wouldn't try to figure it out but bring it to an experienced local tech to do a set up. Fret buzz is one of the mysterious deals the involves a number of different culprits but can always start off with a good truss rod adjustment, pick up height adjustment, a look at the nut cut depth like Raz said.

Things is, at one point I got pretty good at set ups but even then, it would be periodic tweaks and I would still bring it in to be set up every 4ism months.

Thing is, a guitar is a complex assembly of wood, metal, mechanical machining (tuners) and a balance of tension with the strings...The kind of thing I like someone with experience to figure out for me. Set ups aren't cheap and wouldn't need to do it as often as I did but at least set the guitar off down the right path by a pro.