Just got a new to me 03 ranger with a M5od. The transimssion always had this hissing sound when in low gears but I never paid much attention to it since its an old truck. Recently refilled the ATF since I figure it may have never been touched. Aside from missing the drain pan, the job went fine. Took about 2.5-3 quarts to fill back up until the new fluid begn to dribble out of the fill plug. Shifting and everything now feels much better. The only issue is now that sound is now much louder. The hissing sound is loudest in 1st and 2nd gear and is even there when just wiggling the shifter from left to right when not in gear. Funny thing is that the sound eventually goes away with some driving but will return if I put it in neutral and then back in 1st. I'm gonna check the trans fluid again to make sure I didn't mess that up, but wondering if there is anything else I should be looking at. 50/50 on just turning my radio up and ignoring it until something happens.

 

Welcome to the forum

No, not sure what that noise is
Might be the 1/2 shift fork getting worn, it sits on the Dog Gear which is always spinning when vehicle is moving but would have more load on one edge when in 1st or 2nd

If you are not familiar with how manual transmissions work, in a 5 sped there are 3 shift forks, like this: https://www.ford-trucks.com/forums/a...1&d=1501791993
3rd fork is just out of frame
Picture is the under side of the top plate of transmission
The shifter arm moves one of the 3 shift forks at a time to select a gear

The shift forks ride on the Dog Gears which are always connected to output shaft/wheels, here: https://www.ford-trucks.com/forums/a...3&d=1501791993
The 1+2 arrow is pointed at the Dog Gear for 1st/2nd
When you move the dog gear forward or backward it connects to either 1st gear or 2nd gear to get that ratio on the output shaft, when its between the two gears its in "neutral" for 1/2 only, 3/4, and 5/R also have neutral, when all 3 are in neutral then trans is in neutral, lol

All the "gears" in a transmission spin at engine RPM until clutch pedal is dowm
The dog gears always spin at output shaft RPM, wheel RPM
So if there is no noise when stopped but noise only when wheels are turning then could be worn shift fork

If there is noise when stopped in neutral, clutch pedal up, then its a "gear" issue

I would drive it til it drops, lol
M5OD-R1(M5R1) are not hard to find or that expensive used, also reliable so not a gamble with used
You would need a 2001-2008 model from a 3.0l Ranger or Mazda B3000, 2WD, unless you have a 4x4 then would need a 4WD version