98 Eclipse GS
90,000ish miles
Bone stock.

The transmission is making a dull grinding sound whenever it's in gear for the first 20 or so minutes the car is running. Happens in every gear and from 500 RPM to 3500 or so. After the said 20 minutes the noise goes away. If I push the clutch in the sound does go away. The car does not shake, vibrate or do anything else weird while accelerating or driving during that time. No weird clutch pedel vibrations either.

I'm being simple when I say this (as I have almost zero experience with transmissions) but I'm thinking it's just low on tranny fluid. I poked my head down there and see the rubber plug on the side behind the wheel and I'm assuming you can check the fluid level there. I searched around and saw the sticky at the top of the forum so I'll be using the dealer 350 MTX fluid for it if that's the case. Anything else I should look for? Help a transmission dumbass out here.

2005 Corolla XRS
2ZZ 6-speed

Here's how I deal with trans fluid...

After parking the car on a level surface, I remove the rubber butt plug from the side of the trans, and remove the reverse light switch on the top of the trans. It is easier to get a funnel on the reverse light switch, so I fill from there, and fill it until fluid leaks out the butthole on the side of the trans. Put the plug back in, and consider the trans full.

Soooooo you're saying it does sound like a low fluid issue...right?

2005 Corolla XRS
2ZZ 6-speed

no, its your throw out bearing, its dirty.
get new one

I was just passing along how I check the fluid level and top it off.

It does sound like a TOB, though.