Hey guys, I own an Automatic 2007 G35 sedan; here's my exact problem:

Though it fluctuates, whenever I reach approximately 3000 rpm, I hear a rattling or almost knocking-like noise from the dashboard, driver's side. I have heard maybe something is loose? It speeds up as I increase RPM. For the first time since this happened yesterday I got to nearly 5500 RPM with no noise at all, but then it came back again.

Any ideas? It's driving me nuts and I've been driving slowly ever since so I don't stray too far past 3000 RPM. Thanks

 

^^ wow, good call!

 

YOU NAILED IT! I'm so thankful you were able to diagnose that, thank you so much mate! Is backflushing the heater core something I can do at my house?

 

^ you could do at home without much fuss, but as long as youre under 60k/4yr warranty just print out or take the TSB number that trech posted to your dealer and ask them to fix it for free under that, even if youre out of your primary warranty SOME dealers would still performs TSBs for free however most would try to charge you.