There seems to be a knocking noise coming from the top/front part of my engine, but I can't seem to pinpoint exactly where it's coming from. Has anybody heard this noise before?

The sound gets faster as the engine RPM's go up, but doesn't seem to affect the performance at all. There is also no vibration at all.

Not sure if you'll be able to hear it properly in the video, but in person, at Idle it sounds like a marble in a empty beer can being shaken every 1 second. It also reminds me of the knocking sound effect that you hear in a movie when a car breaks down on the side of the road while steam pours out of the hood

https://www.youtube.com/watch?v=GQ0Ij9EpX6E

https://www.youtube.com/watch?v=2-0P84eubFo

The car is a 1983 w123 300d turbo