So a while back (~3,000 miles ago) I swapped a 717.400 5 speed Getrag into my US spec 1983 300D. Everything went well, used a complete donor car so no modifications were needed, I used the 38# flywheel. I was able to drive the car before removing the transmission, but it had a terrible clutch and the engine was definitely on its last leg, so I was mainly just seeing if it would go through all 5 gears.

Ever since installing it, it has a slight whirring or humming noise at the bottom end of what seems like 2nd, 3rd, and maybe a little of 4th.

I replaced the following during the swap-

Slave/master
Clutch disc
Pressure plate
Throw out bearing
Pilot bearing
Trans mount
Flex discs

I'm sure there's more, just can't think at the moment.

I drained the old fluid out (looked like ATF, didn't see any metal, didn't look too dark) and replaced it with some Valvoline Dex/Merc ATF. I have some better ATF on the way that I plan on replacing the Valvoline with.

It shifts totally fine, I've taken it on a 1000 mile highway trip with no worries, but the noise is bothering me

Some notes-

-My fender liners are currently out, and I have 27" mud tires that make a ton of noise, as can be heard in the video
-The Release fork was slightly loose on its ball when I did the swap. Wishful thinking- that's the noise

Here's a video. Any ideas?

https://youtu.be/hX796lPDyN4

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'84 300D Euro 5 spd
'83 240D 4spd
'83 300D/5 spd manual/Lifted+28" AT Tires
'83 300SD
'10 E63

Parting out- '79 Euro 280TE Green/Green & '89 300SEL White/Grey