Dynomax Super Turbo interior sound levels

Hi all. My 1970 Dart 340 has stock manifolds and a 2.5 inch exhaust with an H pipe. The mufflers on the car at purchase are Dynomax Super Turbos. Turn down tail pipes at the back of the car. Exterior sound is great, if not even a bit quiet. Interior noise level is, on the other hand, very loud. I'm going to guess that these have been on the car for at least 10 years, but look very good. Does it make sense that the interior nose level would be so high? I'm talking hard to talk to companions level of loud. Trust me, I love loud motors. My boat has twin 500efis with headers, have owned many Harley's that I piped, etc.. This one doesn't seem to make sense comparing exterior to interior level of loud. Appreciate anything you have to share about these mufflers. Thanks