well, it HAS been located and fixed. A friend of mine volunteered to sit in the trunk and locate the noise, and we got it. After removing the back trunk panel, side panels, and interior roof assembly, we located the noise maker. It turned out to be one of the brackets that attached between the interior "roll bar" frame, and the roof itself. The brackets were TIGHT, but one of them, was adjusted too close to the frame itself-(shaped like an L, and the long part of the L rides on the frame)-and it had worn away the paint as the chassis flexed. once it was metal to metal, it began "popping". I took both brackets out, and lined them with double-sided-tape to fit between the frame and bracket. VIOLA! no more popping!!!