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Yep, take a 1/2 full bottle of beer and blow across the top until it sounds a musical note (you know you have done this). You just found the resonant frequency. Drink some more beer and blow across again. Now you have a larger air volume and lower resonant frequency (deeper note). Finish the beer and shove cotton in the bottle until it no longer sounds/resonates. Now you have dampened the resonant frequency of the bottle.

Most aftermarket exhaust systems use larger diameter pipes and less dampening than stock so the car sounds bigger, deeper and louder. Few spend much time tuning the system to dampen out those resonant drone frequencies. Porsche and Fabspeed do a pretty good job at minimizing nasty 3k resonance through their exhaust system tuning and design. I don't know many other aftermarket systems who do it as well.