ok this just started recently.

going around 45 50mph in 5th gear. when downshifting from 5th to 4th to 3rd gear everything is fine. now sometimes i go 5th to 3rd when breaking again same speeds. LOUD grinding sound. clutch is down all the way when doing this. tried again from lower speeds around 35 40pmh. no sound. its only 3rd gear which makes this nasty noise. going up gears its smooth. any ideas?? car is 09 got about 30k only performance mod is trd exhaust.

 

maybe you need to change your gear oil to something good like eneos