I have a similar problem.

I had the heat shields come loose at the bolts and now have two metal clamps on them. I always wondered if the fact that the shields are now making contact with the converter, if the heat is transferred on and therefore can still start a fire.

I've had the entire exhaust pipe (from the catalytic converter to muffler) replaced just recently. However, whenever I'm at a specific range of RPM (either right when I'm starting to drive before it advances to second gear and then again in between 2nd/3rd gear), it sounds like the area between the catalytic converter and the A-pipe rattles like crazy. I also noticed that if I warm up the car, this happens almost immediately rather than if I driver her off "cold". I can usually manipulate the rattling with the gas pedal - taking it off or pressing it at the right time for it to change - for example: I drive up a hill, top of the hill that area begins to rattle, down hill I let go of the gas (feel the gears change) and the rattling stops. It's gotten worse. Whenever doing highway speeds (70 mph), now there's a constant low pitch rattle/grind like there wasn't before.

I posted about this issue before and it was suggested that it might be a cracked exhaust manifold - my visual inspection didn't find a crack or anything as far as I could tell.

Thanks

 

Instead of messing with the old shield, I just purchased a new one(top & bottom) and 4 new bolts. With shipping and handling, it came to roughly $53. The old shield was rotted away at each bolt location. I thought about welding it or clamping it, however, I opted to just replace it. I may have to lower the exhaust to get the top cover on. I'm going to be tackling it this week and will post my results.

 

You'll probably have to remove the 2nd O2 sensor, which (I think) installs thru a hole in the upper heatshield. I think you need to go underneath the front passenger seat to unplug the wire for that.

 

I had the same problem when I bought my 94 accord, its the gasket where the headers merge to the catalytic converter. I was going to tighten the bolts but they were rusted to the point where it might strip the threads, so I decided to clamp it with a vise clamp. If youve got a vise clamp lying around, tighten it as much as possible and squeeze the flanges together where they meet. I thought it was the heat shield or the cat, but it was definately the gasket, because after I clamped it, no rattling noise! Its lasted since then for a year and a half. And it only happened at 1800 rpm, quite loud too (enough to be embarrased by). Dont use a spring clamp, theyre not strong enough to stop the vibration.

Let me know if it stops the rattling noise, if it doesn't then its not the gasket, could be another part of the exhaust.