Infiniti replaced my transmission at around 15K miles for a transmission with the bad input shaft bearing issue. The noise this failure emitted was excessive gear wine, not a rattle. The noise would change frequency along with my engine speed. Accompanying the noise was grinding shifting from gear 5 to 6. My guess was the extra friction from the bad bearing was interfering with the syncros from matching.

New trans, like the old trans, is noisy at idle when the clutch pedal is not pushed down. 190K on the new one, so I don't care. My long tube headers make more noise, and I like it.

 

Thank you vqsmile and 07-G35-MT/S. I think I was just bugging out because I thought the sound was completely gone after I flushed the tranny. It most likely just gear lash. I am nearly certain it is not the input shad bearing because it does not whine, does not change frequency, and does not grind while shifting. Maybe I'll have to invest in some long tubes