buzz mystery in a '41 kay

[Jack6]

Hi out there.

I have buzz that seems to be coming from the lower back part of the bass- a snary, cidada like buzz that spreads from the A and D into all the notes. I have glued up all the open seams and took it to a very skillful luthier twice- the second time to take the top off and get inside. He sealed up some loose seams in the plywood, eliminated all splinters and loose glue and went over it very thoroughly- it seemed to work for the first two days but now its back. I can tap almost anywhere on the front or back and hear the rattle, but it seems closest in that lower back portion of the instrument. The soundpost was recently replaced and seems to fit well. The are no open seams and the luthier took great care in going over the plywood itself. At this point I feel pretty stumped and stalled out- my recording project and therefore my whole life plan seems to be hanging on solving this thing. Does anyone out there have any suggestions?

-J