Exhaust Leak.....
 

I started up the rex today it makes this low growl from the exhaust, probably at the muffler. Then after I drove it for a while it stopped. Then I started it back up later and it's doing it again, but it doesn't stop. What could this be? Maybe there's something in one of the cats or the muffler....I don't know....:(

Is a low growl bad?

it is if it's intermittent, indicating something is loose or not functioning properly.

Example: Burning antifreeze smells sweet, but just because the odor isn't offensive doesn't mean it's not a symptom of something wrong.