Ive been having a problem with my 3rd gear.
When I shift into 3rd gear quickly I grind my 3rd gear, but when I do it slowly it does not. Its rather strange. I made sure the clutch was absolutely 100% pushed down and everything and still grinded when I tried to shift quickly. If i shift regularly (slow, patient) then it doesnt grind but doesnt slide in so easily. Only in 3rd gear too. 2nd gear doesnt slide in so well either, but doesnt grind. All of my other gears are smooth.

Tranny problem or clutch problem? 27k miles, no tranny problems so far.

 

Synchro problem. The reason it grinds when you shift quickly is that the RPM is higher so it is harder on the synchros to allow a smooth shift between gears.

 

My friend also said he thought it was a synchro problem. How might I go about fixing it? My car should still be under warranty.

 

Nissans method of fixing synchro problems is a complete transmission replacement. I would say most car companies would tear down the transmission and just replace the bad synchros.