Burbling noise coming from air filter box

Hello,

As mentioned in the title I am experiencing a perplexing burbling sound that can be heard from the air filter box when the car is revved at idle.
The noise only occurs once the car has fully warmed up.
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Noise can be heard both inside and outside as shown in these clips.

Disconnecting the intake manifold hose only makes the noise get louder.
I have a long journey ahead of me at the end of this month and I am extremely perplexed as to what the noise is, very worried.

Any help with this would be greatly appreciated.
Cheers.

Side note: I will be swapping out the manifold flaps for new ones later this month.