What make these cars quiet?

Cut the tail pipes off and now it exits right @ the muffler without dumps.. and boy is this car loud like this. Already set off 1 car alarm just cruising.
LORD... i had no idea tail pipes quiet down the 5.0s like mine was.

However, the shop that put my SLP tips on screwed up big time. The exhaust was leaking from the tip area so the sound was already odd and maybe taking away volume.

In this video i was trying to route the exhaust fumes out the garage while burping the radiator.. and you can see the leak big time.