i have seen several 201 and or 124 chassis 5 speeds where the bearing between input and output shafts was obliterated by unlubricated neutral towing. may not be as big an issue on this type of gearbox, but if the car was ever towed in neutral without the countershaft throwing lubricant, the most covered bearing turning at the highest speed is this bearing, which is unfortunately the one most in need of lube and not getting it. i have a horrifying pic of a towing disaster where this bearing got so hot that the end of the output shaft got snapped off in the input shaft.

im always suspicious of this bearing first, because after 30 years most of these cars have seen a tow truck, and people think that putting it in neutral and back feeding the gearbox with spinning the output shaft alone is harmless for some of these cars. works on some, but not others, but every tow truck driver will tell you its fine and argue

depends on how this bearingi s designed on your gearbox, but with the pedal out and clutch engaged like that, path of power would be input shaft ,down to countershaft, and back up to free wheeling gears on output shaft ,so noise could be from bearings for either of those two shafts or gear tooth chipped or something like that.

unless something is horribly wrong ,the reverse gear and shaft should be not touching and idle, so i doubt reverse is related.

the trick is to identify which gears its silent, and which gears some noise but not a lot are happening. for instance, if i had big noise in neutral and power going through like this, but completely silent in say 4th gear at 1 to 1 ratio where input and output are locked together, id be thinking the cause is the bearing between input and output shafts. that would be consistent with when that bearing is turning specifically, and the noise would be loudest in neutral, different in 1, 2 , and 3, quietest in 5th ,and silent in 4th

but say i still had noise in 4th ,then it couldnt be that bearing, as in 4th that bearing is not moving.
in some gears as in clutch out neutral, many bearings are turning all the time ,you can narrow it down some, but either way, you probably should break it open if its a really loud problem.

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