If the airflow is even out of both pipes, I wouldn't worry.
Uneven airflow, then I'd guess you have a hole in your exhaust but after the muffler/reso if there is no sound difference.
It may even be trapped water in the reso which would work as a temp buffer, which is completely harmless.
Not sure why most people say that noise is normal, my dealer said it was bad. If I were you do this:
If you have warranty where the tc (transfer case) is covered, take it to the dealer and ask the service rep to call over the transmission guy (be persistent) to hear the noise. He'll freak out and strongly advise to get it fixed. For me, they ended up replacing my tc and rebuilt my transmission. Haven't had the noise since
If you don't have a warranty then don't worry about it. Enough people on here have the noise as well and it hasn't done any harm.