I'm frustrated with a persistent set of issues with my 2008 Rogue FWD QR25DE that I believe is related to the exhaust.

Issue 1) Rotten egg smell when hot, it emanates from under the car and when I come to stop the strong smell is sucked into the cabin if the HVAC fan is running. Very intense, distinctive rotten egg smell. Exhaust has been inspected twice, no leaks detected. Each time the smell was attributed to "bad gas with too much sulphur". Recommendation - change gas stations. I've tried every type and grade of gasoline over the past 2-3 years and no change, the smell is very consistent. At idle, when hot, if I bring the rpms up to 3-4000 and hold for 10 seonds the smell will be produced every time, but it has to be quite warm to hot outside, in winter and cooler spring days there is no smell.

I understand that if a cat goes bad, the sensors will report exhaust gas out of spec and throw a code. My question is, how bad does it have to get before a code is thrown, and will this particular code trigger a check engine light?

Issue 2) Metallic rattle from under vehicle when hitting sharp bumps. I have long suspected exhaust heat shield, but I've inspected this many times and had the shop inspect at least 3 times and each time they reported no visible issues. I'm wondering if this could be one of the cat converters with loose metal pieces inside that shake around? What is the best method to trouble-shoot a bad cat and get to the bottom of this - the dealer shop just states "if theres a problem, you'll get a check engine light" and that's it.

Thanks in advance for any ideas, much appreciated.

Is the converter removable on the Rogue? You could remove it and shake it around...could have come apart partially, not enough to set a light.

Problem is ongoing, been experiencing it for over 3 years after highway travel in warm weather, the stink occurs more readily now and in cooler weather. No MIL light yet, but I've ordered a code reader and diagnostic OBD tool which will enable me to check for mystery codes and also sensor readings on the intake and exhaust side, maybe that will shed some light.

The Rogue is still running great and getting really good efficiency in line with posted numbers, so perhaps everything is fine, I don't know for sure, all I know is that smell knocks you out and it sucks when you have kids in the car.

Hmm do you have access to an exhaust back pressure tester?