That or the infamous heat riser that is sandwiched between the passenger manifold and header is leaking. The weighted flapper valve has two inside bushings for the shaft flap to rotate on These bores an/or bushings get worn and exhaust leaks through them making a distinctive gurgle. If that is indeed the problem, dissemble the exhaust manifold from the head and header. At this point you can re bush the shaft or cut the flap out and plug the shaft holes via a tap on either side. The last method would destroy they function of the heat riser flap but can be high temp epoxied into the open position and wired for good measure then reinstalled. Hope this helps.