Yeah, sounds like a pre-cat problem to me. My '96 SE suffered it at about 45k miles, replaced under the emissions warranty. At your mileage, you're out of warranty on everything. So I would follow the advice of the previous poster and go with headers and aftermarket everything. Why not pick up some additional power and sound since you have to replace it anyway, right?
This is not something you can ignore - its a problem that needs to be repaired ASAP, or it can lunch your motor. Excessive backpressure can cause detonation bad enough to burn a hole in your piston. There have also been cases of bits of broken precat material being sucked into the motor through the EGR, and sometimes through the exhaust manifold itself during vacuum conditions, particularly on deceleration. Once that happens, it scores the cylinder walls badly, and suddenly you need a new engine.
