I went out for a walk yesterday with daughter & her partner. Near the top of a hill we sat on the short sheep cropped grass to admire the view & get our breath back.
What was the noise? A horse being ridden? Some sort of machinery? It came, stopped, started again. Not always from quite the same direction.
Then we carried on up the hill and saw the answer. A sheep grinding its teeth. Who would have thought it would be so loud. Maybe amplified by the lay of the land.