Bilge Blower Exhaust System

so i bought a bilge blower fan thing and flexible ductwork for my little two plant, four cfl's and homemade reflector grow tent. its loud. real loud. i have tried using insulated 4" duct. i have tried making my own muffler using insulation stuffed inside said flexiduct with holes punched in it. i am looking for suggestions with minimal cost impact as i am broke like that horse from the little rascals. you know the one.

please respond in all caps so i can hear you.
 
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