Razor gang

It's possible the chicks may have hatched but they are hidden away in rock crevices.
The adults are kept busy flying in supplies  They keep up a grumbling chorus of creaks grunts and growls which sound uncanny and unbirdlike, more like a very heavy wooden cart being dragged uphill by a straining horse, or an ancient door with rusty hinges being forced open for the first time in a century.
Like this.

The Finnish name for razorbill 'ruoki' is probably the best approximation of the noise they make.