Sounds pretty aggressive and I have no idea what it could be. 05 Coupe AT

 

That doesn't sound good. Sounds like your rod is knocking. Also sounds like the issue that this member is having. How many miles on your car and are you the original owner?

https://g35driver.com/forums/g35-cou...sure-what.html

 

140k and I'm the second owner. I've had this car for less than 1 year. The knocking is fairly recent but it's not always there. It comes and goes. This time was definitely the loudest and most aggressive I've ever heard. I have been checking the oil level because this car does burn oil a lot. I hope the engine isn't done for because of lack of oil/maintenance

 

The problem with knocking like this... especially at idle, is that it can very quickly wear the journals on the crankshaft and throw them out of spec which generally requires a new motor or full bottom end rebuild.

 

When was the last time you checked your oil level? Never happened to me but that's how it may sound when you're running out of oil.
Gary