I'm wid Sarge on the tube type manifolds cracking....usually around where the tubes all come together. If the noise is from a crack in a manifold, it will
usually be worst when cold, then get a little quieter when hot, as things expand.
If the manifolds are not cracked, and you have trouble keeping gaskets from burning out, try this trick.....use regular paper/asbestos header gaskets. Soak them in water for a few minutes before installing them. Put them on, tighten the bolts, and fire the engine up....let it run for a while, or drive it around the block a couple o times easily. Don't drive it hard...just a nice easy cruise. Hammering on the throttle with the gaskets still wet has a tendency to blow them out....which is what yer trying to NOT do. Then re-tighten the bolts. 99.9% of the time this will FIX the flange leak problem. With the gaskets wet, they are softer, and will compress, conforming to bends in the flanges far easier than if they are dry. Once you heat them up, and dry all of the moisture out, re-tightening the bolts will completely seal the surfaces.
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Joel Adams
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