Volvo Repair: Volve 740 rattle, catalytic convertor, volvo 740

Question
My 1990 volvo 740 will not stop rattling under the car, it rattles on ignition, and
whenever im going slow, i saw in another question that it could be the exhaust
pipe heat shield or the cat converter, if it is one of these, how could i go about
fixing it?

Answer
  Miles, most common is the catalytic convertor. The guts break down and melt. The only authorized fix is replacement. They are expensive. I've heard of owner's removing the Catalytic convertor and and jamming a metal rod through it and "hollow" it out. If a "shop" does it, it is a $10,000 fine. If the owner does it....????? It's just a rumor and nothing I advised you to do.......

Mark