Edit: The issue turned out to be a bad catalytic converter and will be replaced under warranty. Here is a link to check if your G37 is still under warranty https://www.motor1.com/reviews/39682...%2C000%20miles

Today I noticed a sound coming from my car I’ve never heard. Stock 2013 sedan. Definitely sounds like knock from my understanding. Is happening mostly between idle and 1200 rpms and will fades in and out. It sounds the most prominent from the exhaust exit on the passenger side of that helps. Listening from underneath the car it’s much louder and makes it at startup and shutdown after being warmed up. Oil levels don’t seem to be out of spec. I can hear it when stopped but I don’t hear the sound while driving, however
its 10 degrees and snow is on the ground in Dallas right now, and I’m not sure if knock would be loud enough to be heard over snow and ice crunching. We definitely don’t know how to deal with this weather... hopefully the Infiniti dealer is open tomorrow.



engine bay

 

That's doesn't sound like knock. More like a heat shield hitting your exhaust ,not too sure but not knock

 

What does that mean?
Did you check your oil first thing in the morning after sitting overnight parked on level ground? Does the oil level show full on your dipstick?
Are you using the recommended 5w-30 oil?
It sounds like a rod knock to me.
Get it checked out
Good luck

 

IME rod knock gets horrifically worse higher in the rpm range and especially under power.
Could be cat shield noise or exhaust knocking around. Could be valve train related. The marbles in a can sound isn't good though.
Take it to a good indie to get checked out.

 

Either a heat shield or the cats are rattling. Had a sound like this but not quite as severe, turned out to be my secondary cats in the catalytic assembly

 

The oil level is between the 2 hole cutouts and closer to the 'H' end while cold.
I do use 5W30 but with it being 5 degrees F outside I wonder if it may just be that the oil is not up to temp yet.
I feel like that's probably just wishful thinking though.

 

I have a similar sound and a cat code. I'm thinking cats. An oil analysis will say for sure.

 

Update: not sure what the knocking sound is but my oil is looking nice and milky.

 

Meaning you have water in your oil and it turned white? If so, two days before it wasn't when you checked it?

 

It was not white. I had checked it and noticed a slight resin effect on the dipstick (like the flow in an acrylic resin art piece) but it was very slight and there was no discoloration so I didn't think anything of it.
Two days later and the car hasn't been driven since after sound began but has been started 3 times to scan for codes and check fluid levels after they all heat up.
In that time the coolant level has slowly gone down from halfway between min and max to sitting at min. Took off the radiator cap found air bubbles in the coolant.
Checked the dip and the oil looks fine. Started it up and checked the oil fill cap and milky oil was splattered all over. Having it towed to a shop tomorrow.

 

Obviously a head gasket issue, maybe the knock you heard was simply a misfire due to slightly cracked head gasket which completely failed later? I once had a head gasket fail in between the cylinders where there were no water channel. It was missing badly on both of those cylinders but oil was clear, it was a pain to diagnose until I checked compression.

 

Possibly, not even sure what the issue is anymore as the shop told me shortly after I dropped my car off that they couldn’t hear the knocking noise nor found any water in the oil despite me having seen it on the oil cap. Maybe condensation and it evaporated off? That doesn’t resolve the coolant loss issue though. I guess I’ll only know for sure once I have them do an oil analysis and compression test. Crossing my fingers.

 

Ohhhh on the oil cap??? I missed that. Yes that does occur sometimes and is nothing to worry about. The noise that you posted didn't sound like knocking to me. More like a rattle or vibration. Maybe a tensioner pulley, or maybe a catalytic converter or some heat shield got lose. Did you go over some speed bumps and scraped recently? I hope nothing major wrong with your car, how many miles does it have?

 

phew! Puts my mind at ease to know that now, thanks. My first thought on the rattling was that some chunks of snow pulled an exhaust part loose then I checked (edit: the rhythm of the knocking and decreased fuel economy made me think misfire/rod knock) the oil and my heart sank. Hopefully all is well, odometer is only at 68k and bought it with 53k back in June.

 

Here's a decent article about milky oil under oil cap: https://dannysengineportal.com/white...-it-is-it-bad/
Your mileage is low, so I think you're fine. But I suppose we will see what they say. I've mostly seen blown head gaskets (and experienced) with mileage north of 120k after hard driving. Keep us updated though!