"Umph" pronunciation?

Hi! everyone.

Could you tell me what "umph" means or expresses in the following para?

Chips would say, punctuating his remarks with that little "umph-um" that had by then become a habit with him: "Colley, you are—umph—a splendid example of—umph—inherited traditions. I remember your grandfather—umph—he could never grasp the Ablative Absolute. A stupid fellow, your grandfather. And your father, too—umph—I remember him—he used to sit at that far desk by the wall—he wasn't much better, either. But I do believe—my dear Colley—that you are—umph—the biggest fool of the lot!" Roars of laughter.

Thanks.