The noise that Jake could hear was the sound of K9's whirring motors and his wheels moving along the ground. Doctor Master had requested that he change his primary assignment to locating a human female known as 'Abigail Hobbs' who was in danger.
K9 had widened his sensor range to pick up human lifesigns, eventually getting a reading, although it was weaker than expected, unless the human female had been weakened by an injury of some kind. As he trundled forwards he picked up a second lifesign.