Wasn't that a clicking sound in the transmission shaft?

And the motor temperature?

Heat began to close in.

Driving ports were wide open, the turret was open, the fan was rotating; yet it was growing hot rapidly. Dennison mumbled to himself about the vents. The roaring of the treads knocked the roof of his brain; he felt that the old deafness was returning.

When gasoline and oil fumes increased he let up on acceleration but not before Zinc came down with a harsh coughing spell.

Fear came ...

It crawled along his spine, yesterday's fear, last week's, the past mucking up death, Robinson's arms in the sand, Al screaming, a village gouting smoke and fire. He saw, as in another world, another man's world, his years in Ithaca, at Cornell. The bronze figure of Ezra Cornell was hazed by leaves--then blurred by falling snow. He saw tree-fogged paths winding to his flat on the hilltop above Cayuga. He saw the lake gleaming, blue as a smudged blueprint. He saw himself rowing with the university crew, his body synchronized to the dim bodies of his mates: Locksley ... Neilson ... Murphy ... Lee ...

Lee was coxswain:

Steady boys, steady now ...

But all this was dead: his mother was dead: Aunt Therèse was dead, Uncle Victor, Landel and Zinc were dead: all were travelling through a fog, a distant fog.