1975 Chevrolet Other muffler

1975 CHEVROLET
556,000 MILES • 4.7L • V6 • 4WD • MANUAL
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KRISGO
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my truck is making a loud noise sounds like it may be coming from the muffler its like a rattling noise. my question How can i tell if it is the catalyst or muffler?
Oct 10, 2015 at 12:40 PM
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CARADIODOC
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A loud rumble is due to a leak. You're going to have to crawl underneath and look for that. There could be a hole in the catalytic converter, but those don't corrode very often. It's much more common to find a hole in the muffler, especially if there wasn't a tiny drain hole at the rear / bottom.

Some catalytic converters will rattle or make a thumping sound when the catalyst breaks loose, but in '75 GM used small pellets, not a solid substrate like everyone else used. Those pellets won't make noise.
Oct 10, 2015 at 10:19 PM