Bill Griffiths in 'Fishing and Folk: Life and Dialect on the North Sea Coast' (2008) describes two similar local features: 'Rumble Churn' at Dunstanburgh and 'The Churn' on the Farne Islands.
The latter feature is said to be a cavity in the rock near the north-west point of Inner Farne. It has a hole at the top through which the water is forced by the sea, producing a beautiful 'jet d'eau' (water-spout), particularly when the wind is from the north-east with a heavy swell. Presumably, he says, the noise resembles the rumbling sound of a churn.