Hm... Make sure the locking nut is tightened as tight as you can get it. The purpose of it is to hold the strings tightly so they stay in the tuning that you put them in... Another thing is... tuning the guitar down to drop D is probably what is causing the fret buzz... You're probably using light guage strings with a low action set-up... and any decrease in string tension will cause fret buzz... I suggest getting a larger gauge string set... This will counteract the detuning fret buzz. Also, moving the saddles back and forth won't change the action, just the intonation... and this could be part of your tuning woes. Unless you know how to adjust intonation I would suggest taking it to a tech. I could explain how to do it but that doesn't mean that's neccessarily the problem. In order to effectivly fix the problem that you have I would have to see and play the instrument... So in review...

1. Tune the guitar to standard tuning...
2. Install the locking nut... make sure its super tight
3. Drop the E sting to D tuning
4. Adjust the trem springs appropriately
5. Adjust the E string Saddle up as needed...

In the long run if this doesn't help at all... I would say take it to a tech a get a set-up... Use larger gauge strings so you can go between Drop D and standard without bottoming out on the fret board.

Good luck