3rd to 4th gear grind.
 

When ever i am driving and i am in 3rd (at any rpm above 5 or 6) and i shift into 4th, i hear a gear grinding sound and feel the shifter not want to go in, but its not hard to over power the shifter. I have my foot all the way down on the clutch when i do it.

Altho shifting into 4th at a lower rpm(normal acceleration) i don't hear or feel any resistance on the shifter.

any thoughts on what this is?

And once i am in to 4th gear its fine.

search.

I got a new transmission 2 months ago because of this very issue.

what caused it?

rx8 tranny sucks.

when should i take it in. like should i take it to the dealer now or wait till ______ happens?

take it in now. make sure you keep the service record if they claim could not reproduce the issue. Then bring it back a few more times with the same issue till they find it. If they do not find it and down the road you are out of warranty, you'll have a paper trail to show the issue and your attempts to get it fixed.

if your dealership is worth it's salt, it will verify the problem and resolve it for you.

I just started getting the EXACT same problem. Usually shows itself during "spirited" backroad driving.

follow what mysql saids.