He probably would even have noticed the Doctor tapping away if he'd got the rhythm right, and in time. As it was, the tapping beat counter to the beat in his head and he couldn't help laughing, as he followed the Doctor round the corner.
"Oh, Doctor," he said, almost fondly and a tiny bit hysterically, "you really are ridiculous! Trying to keep my drums company? You've got the rhythm all wrong, for a start."