I had a ford that catalytic converter sounded horrible.  It got worse
with increased rpms.  It was the heat shield.  There were four weld
points that held it to the cat, and created the air space to protect
the ground from it's heat.  Well two of them failed at once, causing
it to vibrate and hit the cat.  I had it rewelded once, failed again,
so I fixed it myself.  I went under and pulled the shield far enough
away from the cat, so it could vibrate, but not constantly hit the
cat.  Only needed a 1/4" seperation.  It worked.

hope this helps,

tom

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