There's no doubt that pressure changes do occur in an exhaust system. Witness what happens to performance and fuel economy when the exhaust becomes perforated. The thing sounds and runs like shit. The engine relies on acertain amount of back pressure from the exhaust gases that are trying to escape.
I like that theory from Peryn. The fact that the noise is at its peak during the actual act of shifting, ie where revs drop substantially before being picked up again (albeit at a lower level) by the next gear engaging would tend to validate the "Peryn theory".
Any advances on that fellas?
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