Shifting Gear 1->2 as RPM decreases
 

Hello,

So from time to time I would get obnoxious rattles when shifting from gear 1 to gear 2. I didn't know what was causing this and I didn't know how to recreate the phenomenon. It simply happened on average of once or twice during each of my driving sessions. I thought something was wrong with my car.

I finally figured it out today. I was able to replicate the issue. The rattling happens when the RPM is decreasing during the shifting from gear 1 to gear 2. So, I have to either shift 1->2 at the exact climax of the rpm or when the rpm is increasing.

Is this the only cause of the rattle? I don't know. Maybe others can share what they've discovered.

My car is the '13 G37S Coupe 6MT.

Rattle? As in two loose pieces of metal hitting other? Or detonation?

Like a lot of things on the under-carriage shaking in an unnatural way. This is for the coupe. Specifically the Sport version. I don't know if it's only applicable to Sport or the coupes in general. I made a recording but the recording hides the rattling noise with all the other background noises.

The only rattling reports on the G that I've seen deal primarily with loose cat heat shields or detonation from running 87 octane gas. It's strange you report it only during the 1-2 shift.

Well, this is really easy to recreate. I've done it on two G37S 6MT's now. In 1st gear, accelerate to like 3k RPM, and let it idle for a second or two until the RPM starts decreasing before shifting into 2nd. Then you'll hear it.

If I'm in first decelerating and hit the clutch i get a rattling too. My car has always done it, never really bothered me. I just make sure i overlap just slightly with the gas pedal when going to a stop in first. I also need to replace every mount on my car so i assume that might have something to do with it.

More than likely you are hearing the dual mass flywheel rattle.
This is normal for our cars and nothing to worry about.