I own a 2010 G37 Sport sedan (automatic) and for the past few years I’ve heard this random loud rattling sound upon her shift from 1st to 2nd at about the 3/4000 rpm mark. Comparable to a cowbell, it only rattles for a solid second or two and it doesn’t effect the performance in any way, it just rattles loud af. Whether the engine is warm or hot off the freeway, it randomly happens (about 2-3x a week) after coming to a complete stop.

I tried to pick the brain of a service associate at Infiniti and she asked about the type of gas I used. I explained that usually use 91 Octane from Mobile1 and she gave me a nod of approval. When asking if it could be a heat shield issue, she just smirked and said “we’d have to check it out” so I agreed. And of course, when the technician took it out for a spin, it didn’t make the sound.

Can anyone please tell me what this rattling might be?!

I’m having trouble posting the vid but here’s the link:
Please check it out. Thanks in advance

 

In park, if you rev the engine, can you hear the rattle as the RPM's are falling back down? Could be a rattling heat shield or loose material in the cats. Both are very common.

 

My bad, a little late on the reply. Thanks for the advice and info. I tried some revving in park but didn't hear the noise. I've never felt any kind of change in performance because of it. It's usually after the engine is warmed up. I'll be heading to work in the morning, exit the freeway, come to a complete stop, and from 1st to 2nd....RATTLING for a solid second or two, and then it stops. Though I never let it rattle any longer than that. To make it stop, I simply let off the gas a little and then it's gone. I need to look further into the possibility of it being a heat shield issue. I'm hoping there isn't something loose in the cats cause that means replacing, right?

 

It sounds like the engine pinging. I had that noise in my G37 as well and it would happen at relatively low speeds like you mentioned. It seems to occur only when the engine is under load and it will not happen in free revving in neutral. I was never able to resolve the noise, but it never happened when it was cold outside, only when it was warm, so that's what leads me to believe it was pinging. It was annoying so I feel you on that.

 

my car has done that for a long time now. super annoying. it got worst after i tuned my car almost 6mos ago. it happens when i roll into the gas @around 2000rpm to about 2500rpm in any gear. it's most notable in first and second gear. it's also the worst when i'm in performance map vs fuel economy map(ecutek). car runs great otherwise.