The metal ball end of tape wounds touching the bridge should provide an earth contact. If the bridge is not earthed properly, buzzing can occur.
It can also occur where dimmer lights or fluro lights or 3 phase power or electromagnetic interference or a fridge on the same circuit or an electric motor or (insert a miriad of things) happen.
At a gig in Europe, nothing got rid of the buzz. To fix it, I taped copper wire to the bridge. The other end, I taped to my belly. By becoming the earth, I stopped the buzz. (Removing the tape afterwards ripped a few belly hairs but was a small price to pay for a fun gig)
I recently did the same in a friend's studio with a similar problem.
The bass doesn't buzz in my studio or at most gigs.