Ok. First change the oil. It never hurts. Any 80-90 or there about. Don’t waste money on synthetic or expense because there might be an underlying problem yet. Just fill it tell it comes out the side hole. Be sure to remove the full plug before removing the drain. Sometimes it can be stuck and then you don’t have anything in the box.
now to find the the noise.
#1: it goes away when pushing on the clutch?
#2: how high off the floor does the clutch disengage when pushing on it?
#3: how high off the floor does it start to grab? ( 2” is the sweet spot.)
#4: does it make the noise in in all the other gears but 4th, or is it gone?

im sure the other members know where this line of questions are going.