I recently bought a 2015 STI after owning a 6MT B7 Audi S4 (V8) for many years. I loved my S4 but it started to nickle and dime me so I decided to go with the Subaru STI.

Following my purchase of the STI, I started noticing a 4th gear grind when the car warmed up (approx 10-15 min). When the car was cold gears 1 - 6 all shift great. Once the car warms up the 4th gear grinds every time. I do not beat on my cars so I don't think this is due to abuse. I also have a long history of driving manual transmissions. I have never owned a automatic car in my life.

With all this being said; I am currently under warranty and I am having my car looked at by Subaru. I am posting this video to see if anyone else has had this problem and could possibly shed some light on the situation.

My 2 cents: I think it's the 3rd to 4th gear synchro. I have tried rev matching with no luck. I have also tried double clutching. "Clutch in - shift to neutral- clutch out - clutch back in- shift to 4th- then clutch out." When I double clutch it usually shifts fine but this is still not right. Also, the only mod to this car is a Invidia catback exhaust.

UPDATE: After the car being in the shop for 3 weeks I finally got my car back and it is running great. The Subaru Dealer replaced the 4th gear and 4th gear synchro all under warranty. I am very pleased with the results and now there is no more grinding.

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