Ben wrote:
Unfortunately I suspect I can't hermetically seal the door to my
airing cupboard :-)

no, but even foam druaght excluder might help quite a bit. Rubber
underlay is quite good for absorbing noise if you do want to line the
walls/door, it cut doen the noise from our CH pump when I lined the
false bottom of the airing cupboard at put a pad of it between the pump
and the wall.

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