gears

I've got a 2010 WRX and it always grinds when I am going from 3rd to 4th when the revs are 3k or higher. I'm thinking it could be the synchros? I don't wanna pay to have the tranny pulled if I don't need to. Anyone have any ideas what else it could be?

first time i post i have a 2017 wrx with 90,000 km as of 4 days ago when ever i shift into 3rd or 4th or 6th it wont go in all the time or unless i move it in a certain position, also does it when its off wondering if this synchronizers issue or clutch or something else no grinding noise or any...