Muffler recomendations?

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I just bought a 1969 SS350 Nova with the most perfectly done 2.5 dual exhaust system I have seen. The problem is at idle the sound from the mufflers resonates through out the interior and you can not hear anything else including the engine idle. I am not sure of the manufacture of the two mufflers but they are square with a diamond plate case. I usually run a Flowmaster crossover muffler with 2.5 exhaust and I wanted to try the Pypes crossover system in the future but I would hate to change over this complete exhaust system just because I need a different mufflers. Does anybody have any suggestions?