Grinding Noise
 

So I recently bought a ranger from a friend, 5spd manual, 186000 miles, and I noticed a grinding noise which started about a month ago. It only happens when I have the clutch depressed. I recently drove the truck from Tucson to Phoenix which was when I really started to notice it. One of the things that is throwing me off about this is that when I first begin to drive, shifting seems fine and there is no grinding noise, but the longer I drive the harder it becomes to shift and the noise progressively gets more frequent. When I parked the car in Phoenix and let it sit for while (about 1 hour or so) I got back in and noticed that the sound was gone and it was easy to shift again. So it seems to get worse as I drive it, but when I let it cool down it gets better. I tested to see if it was the transmission by shifting into gear while the engine was off; after recently driving it, it was impossible to shift into any gear except for reverse, but again after an hour of being parked, it shifted into all gears with ease.

According to the previous owner, the clutch assembly, master, and slave cylinders were all recently replaced. As far as I can see there is no leak in them either, all of the fluids are good as well. Could be a bearing?

Sorry for the lengthy post, let me know if you guys have any ideas, I don't want to spend money fixing the wrong part.

If the noise only happens when clutch pedal is down, then it is the throwout bearing on the Clutch Slave cylinder.
To double check this, after things are warmed up and engine running, push the clutch pedal in while stopped, see if you hear the noise, if no, then shift it to 1st or any other gear and see if the noise comes then.

If you get the noise as soon as the clutch pedal is pushed down it is the throwout bearing, maybe pilot bearing but you will replace both in any case.
Warm and cold could just be the thickness of the grease in the bearing, it is a sealed bearing, as it warms up it thins out so bearing gets looser and makes noise

A bearing in the transmission would tend to make noise when under load and it wouldn't be tied to clutch pedal position, it would make noise when wheels were turning since they can not be disconnected from the transmission, it isn't off the table but just unlikely reason for noise.
When trans is removed to replace throwout bearing you could pop the cover and have a look inside, refill with fluid before reinstalling, it's easier.

Since throwout bearing is fairly new previous owner may have used "less expensive" replacements, so I would replace slave and pilot bearing as well, also check out the thickness of the clutch disc, measure new one at parts store, previous owner make have exaggerated length of time since the new clutch went in.

Thanks, I will look into the bearings. Hopefully that's it

Pilot bearings cost 3 dollars guys.
 

Had the same sound as listed above, griding/chattering noise with trans in any gear or neutral and clutch pedal to floor. Sound would build over time as the clutch pedal was down. Come to find out, the needles in the pilot bearing was non existent. They cost 3 dollars and autozone rents a puller. Cheap insurance.