Whine soind when accelerating, can't find the sound.

[Ninhow]

I'm currently learning to do mechanical work on my E39 and slowly restoring it. I've encountered a potential issue that I suspect might be related to the wheel bearing. I've noticed a small whining noise that seems to be coming from the engine bay.

Here's what I've observed:

The noise only occurs when I'm accelerating in low gears.
It doesn't happen when the car is stationary, even if I switch gears and rev the engine.
One important detail is that I recently had the transmission oil changed by a mechanic, and I noticed this sound appeared the day after.

Has anyone experienced something similar or have any insights on what might be causing this noise? Any advice would be greatly appreciated!

https://www.youtube.com/shorts/p3WjU4qII_k (Sound)

I Appreciate any tips of where to look.