Hi,
Commonly, it is a heat shield on the exhaust system. The spot welds break allowing it to rattle. Also, it could be the internals in the catalytic converter has come loose.
Here is what to try. Take a rubber mallet and tap on the exhaust to see if you can recreate the noise. If you can, have a helper locate where it is coming from.
Now, I attached two pics below. A short while back, there was a technical service bulletin regarding a heat shield weld breaking and causing noise. The first pic shows the affected heat shield, and pic 2 shows how Nissan recommends repairing it. The pipe is under the vehicle approximately where your feet would be above in the driver's seat.
Let me know what you find or if you have other questions.
Take care,
Joe
Images (Click to make bigger)
SPONSORED LINKS
Wednesday, February 5th, 2020 AT 8:27 PM