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They should get louder like others said with miles I had magnaflows on my Truck and they where super quiet at first after just a few miles on the exhaust she started to get her rumble! Wait it out and then see what you think!
like said above they take time to break in. i have experience with GTAs and Macs, both them were very quite and took several thousand miles to break in nice. Give it some time, they will get louder and have a nice tone.