For a couple of days now, when I start the car, the engine makes a little louder noise. While driving, exhaust (at least in the back of the car) makes different sounds, kind of like those sports car make. There is no check engine light.
No smell of gas in the car
The car drives normally, no loss or reduction in power while driving.
No vibrations of any kind
No rough idle.
What could it be? Could it be a hole or a leak in the muffler or something?
That would be my prime suspect. Because that type of problem could result in odorless but deadly Carbon Monoxide seepage into the cabin, this is something that needs to be checked a.s.a.p.
Until you can get to a mechanic, be sure to drive with the windows open.
A muffler/exhaust leak would not result in a lit-up CEL.
Since your leak is located in the rear,you won’t smell much exhaust fumes.To find your leak,plug the tailpipe with a rag and look near the muffler area for any smoke coming out of there.It could be a pipe or the muffler itself.I usually fix these with a piece of alluminum tape and muffler paste until I can get it fixed by a muffler shop.