My G35 has been having an issue and I believe it may be my transmission. I drive a 2004 Infiniti G35 Coupe rwd with an automatic transmission. It has had a problem for the past few months during start up and especially during cold starts. It makes a grinding noise for about 1-2 seconds and the AT Check light will be one and then go away when the sound does. This has made be worried but I wasn't extremely worried until a few days ago when another issue I believe this is related to happened, I was accelerating and tried to go a little faster when the car downshifted and suddenly a loud grinding sound came from the car, it sounded like a gear grinding against a chain it had slipped off of, and I lost all transmission of power, the car's slip light started flashing and the engine rev'd higher, I let off of the gas and the slowly lowered its rpm and when it got to a low enough level, whatever slipped off caught again and the car went back to normal. At first I thought it was the timing chain because of the start up sound and a faint grinding sound from the engine bay that sounded like a chain hitting the walls of the engine but after this incident I'm thinking differently. Any help would be very much appreciated, I'm thinking I am going to need to replace the transmission completely

 

pull the codes from your car. it will prob point you in the right direction. report back once you get the codes and we can try to help you out.