It shouldn't sound at all! That box at the back is called a "silencer". Get it? It's there to stop you annoying people...
rumbling, go to youtube and search for motorcycle exhaust to get a better idea
exhaust tip or glasspack it
By adding a dual exhaust and/or exhaust headers either short or long tubes for sound and performance
Put in a Borla cat-back exhaust, you will be greatly satisfied.
Attach a bigger sports exhaust, simpler enough
buy a performance muffler
because of the alternator drive belt loosing
Oversized exhaust, headers and/or different mufler.
Make what sound louder? Your engine? Fit a different exhaust system. with a bigger bore.
mufflers are an option for sure. your car will have a different sound with a good one. Though full exhaust systems are always better but it's always a matter of money..
The point of a car amplifier is the make music sound better, so in most cases all amplifier make music sound better.
It can be a hole in your exhaust system or it can have something to do with your engine.