Freelander 1 The Duck Sound. Remind Me Please.

Hello all.
Recently re- piped the turbo vacuum pipes in silicon and looks very well. Problem is, because its been so long since I did the EGR bypass I have forgot which pipe to plug to stop the Duck noise.
The thread on the subject of EGR bypass is very long and thought this would be a quicker route.
Also, what causes the sound?
Thanks for your time and replies on this.
Cheers.

https://www.landyzone.co.uk/land-rover/where-does-this-go.223312/#post-2536215
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as to what causes the sound .. could only speculate
air replacing vacuum flowing through a resonant orifice
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atb
`s`

Cheers Sir.
thanks for the reply. Very helpful.
Gary.