Problem with buzzes of this type is that, all too frequently, they originate elsewhere along the string path (tuner, nut, fingerboard, etc) but seemingly manifest themselves or appear more pronounced at the bridge. It's like looking for a cricket in a room. From your description, you've double-checked the bridge hardware so I can only make two suggestions with that in focus:
*Make sure your bridge saddles are level / parallel with the bridge's baseplate so the height adjustment screws are in full contact.
*Re-set your witness points at both the nut and bridge.
I know there are other ways to eliminate the bridge as the sole culprit but they escape me at the moment.
"...my whole body's a weapon" - Luther Heggs