I have a 2006 g35 coupe with 56k miles. I notice a clunking or knocking in park and neutral only. Put the car in drive and it sounds normal. Any ideas. I'll try to post a link to a video later.

 

Is the noise coming from the engine, transmission, other part of the car or do you not really know?

 

I work at a used car dealership and we had a similar issue with an early 2000 model Tahoe. We thought it was a motor knock so we replaced the motor. Started it up and it ended up being in the trans. Not saying 100% that's what it is. But I would definitely look into it
Edit: Also depending on the what type of knocking you're talking about, it could be a worn motor mount