Weird thunk when pressing clutch, Help!

[19birel]

So I've noticed that at relatively low speeds, when changing from 1st to 2nd, there is a "thunk" noise when I depress the clutch. I don't feel anything through the pedal, and the car doesn't jolt at all, there's just the noise. I have searched everywhere and the only info I found was on an E36 BMW M3 forum which said the issue could be solved by changing the gearbox and diff fluid. My car could probably use a gearbox oil change as when it's really cold, I have to double clutch to avoid grinding second gear until it warms up, I haven't really looked into it, but I'd assume that the diff fluid would probably need changed as well. Do you guys think the thunking noise is related to that, or do I possibly have a perished gearbox or diff mount causing the issue? I know my Golf is due for a gearbox oil change, but it doesn't make a thunk, then again, fwd Golf and A4 Quattro, Apples and Oranges.

Any help is greatly appreciated!

[bmos]

Check your axle and driveshaft CV joints and the center driveshaft u joint for play.

The best way to help the 1-2 shift without installing new updated synchros ($$$!) is to use Fuchs Titan trans fluid.

[19birel]

Check your axle and driveshaft CV joints and the center driveshaft u joint for play.

The best way to help the 1-2 shift without installing new updated synchros ($$$!) is to use Fuchs Titan trans fluid.

Yeah, the only time it grinded 2nd, it was 12degrees out so I think a fluid change will solve that issue as I doubt the PO changed it and otherwise it's been very smooth. I'll check the axles for play, but (and I forgot to mention this initially) the "thunk" goes away once the car is warmed up, if it were axles I'd imagine that the thunk would always be there. I'll still check the axles anyways though just to be safe.

[bmos]

Gear oil doesn't flow as easily when warm (that's viscosity) so if it were your trans/diff that would explain it.
CV grease might behave similarly, I'm not sure.

[Davdraco1]

I would check all your drivetrain mounts for wear and tear.

[19birel]

Gear oil doesn't flow as easily when warm (that's viscosity) so if it were your trans/diff that would explain it.
CV grease might behave similarly, I'm not sure.

I would check all your drivetrain mounts for wear and tear.

I'll check all the mounts this week and see if there's any wear, I plan to change the trans & diff oil when it get's warm anyways so if any mounts look to be on their way out I'll swap them out when I do the oil. Thanks guys!

[bmos]

Mounts definitely wouldn't be affected by whether the car was warmed up but inspecting yours and replacing the bad ones is a good idea anyway.

If you do engine mounts you want to really avoid loosening the subframe (at all) and should have the car level while you do them.
If you loosen the subframe there's a good chance you'll mess up your front alignment (cross camber especially)

[Davdraco1]

You don't need to loosen the subframe to do engine mounts. Just have to remove the sway bat bracket and your done in 15 mins. Also, I've had the rough 2nd gear when it's cold but never had the thunking noise from it which led me to mounts. Maybe the cold has torn a mount. Regardless, good luck with the fix. Let us know how it goes.