I've got this weird noise from the rear of the vehicle on startup. It is random and does not happen everytime. I used to think it was related to a cold start until it happened after just 30 minutes or less of the car being off after driving it. I also have PLENTY of cold starts without the sound.

The car is in Park, and I when I start the engine, I hear a noise from the rear. I'd describe it as the sound a transmission would make when put into drive if it was a little stubborn (a clunk sorta sound). It only lasts a brief moment, and doesn't come back while driving. The car has no trouble when driving. It also happens when on an incline or flat.

I spoke to an Infiniti service writer on the phone, and he doesn't think it's anything mechanical. With the car being in park, he told me the rear diff isn't engaging at all, so it's not a sound from the drive train.

Is he correct? In Park, is there anyway that any of the drivetrain would make a sound in the rear of the car on startup?

He suspects that maybe something in the exhaust could be loose and the heat from starting the car is causing an expansion. I want to call BS to him as I can't see enough heat being generated on startup to cause somehting like this.

Since I can't reproduce the sound, my thoughts are to video tape my start-ups for the next couple of days until it happens again. Then I can at least document the occurance. This seems like it would be a PITA, even with a tripod. I'd want to have the camera as close as possible to the area where I think the noise is coming from. If it's not central, then it's more on the passenger side.

 

Drivetrain no. Exhaust is possible but a bit of a stretch. I'd lean towards pressure building or relieving in fuel tank or related. Clunk heard possibly from the filler neck? Passenger side rear, makes sense being filler door is right there. Video would be good. Maybe remove gas cap, start car & see if noise is heard. Good luck.

 

I have heard this clunk with my car but it only occurs when I'm parked on an incline and I'm shifting from park to reverse on the 7AT.

I usually always engage my parking brake while still in drive and then shifting into park. This puts the weight of the car on the parking brake and not the transmission and drive train.

Interested to hear more or if you can possibly capture a video of the sound.

 

Could it be the ABS system check? Used to hear it loudly on my G35. Not so much with my G37.

 

Parking brake noise.

 

The salesperson said the same thing, so I started making sure the parking brake was off before starting the car. It still happens even with this extra step.

Do you think it matters that I disengage the brake before starting, or once the brake is on, something about the function makes it cause that noise even is disengaged before startup?

 

I think I may have solved the problem. Time will tell. This weekend, I discovered that my mufflers weren't in the brackets properly. I made a thread about that as well:

https://www.myg37.com/forums/g37-sedan/262889-stock-muffler-mounting-holes.html#post3843656

I'm hoping this was what I was hearing and now that I fixed it, I hope not to hear that sound anymore.

 

If this does solve the problem...i guess the service tech was right!

 

I'd say he's half right.

When he first mentioned exhaust, I asked him if he meant the exhaust was making noise from the vibration of the engine starting. He clarified by saying "no", it's from the heat causing it to expand.

I can't imagine there's enough heat generated by the end of the start up of the car to cause the exhaust system to expand enough to make that sound. This sound would occur within 1 second of pressing the start button...right as the engine cranked up.

I haven't heard it since I fixed the muffler mounting (Tuesday). I think it's done. By the weekend, I'll be 100% sure. Other sounds from the rear have also stopped.