I recently had this problem and its very weird. I only have 10k miles and my 4th gear already grinds. The thing is it only grinds sometimes. Dont worry im not a stupid newb and i did search. The problem is when im on the highway or city and cruising and put it in neutral and coast for a little bit in neutral then trying to put it into 4th it grinds and wont go into gear. Also sometimes when i skip from 6th to 4th it will grind too. I usually dont skip gears but only when i need too. Some help will be appreciated. Thanks in advanced.