Random buzzes that are not due to string height, nut, or frets:
- Tuners
- Tuner buttons
- Strap buttons
- Bridge springs
- Pickup springs
If there is a screw on the guitar put the proper sized driver in it and check it. If that doesn't fix it, it might be the tuner button. Check each one by holding the button while plucking the open string.
Old style riveted elephant ear (Fender) style tuners can be immobilized with the judicious use of CA glue. One drop will do the trick.