Oil ventilation causing worrying noise

The car is a 2001 Ford Mondeo with a 2.5L V6 Duratec. The hose that goes from one of the heads back to the intake (oil ventilation) had a worm clamp in the middle of it, ‘strangulating’ it. The hose itself was fine, so I removed the clamp to see what would change. The car then started doing the noise you can hear in this video.

I asked the previous mechanic why did he add the clamp, and he confirmed he was the one that added the worm clamp to fix this exact problem, but he has no clue as to what actually causes the noise. The clamp was a band-aid for the noise.

Does any of you have a clue of what this may be?