What was "rolling thunder" and why did it irritate friendly troops?

The rolling thunder was the bsttery heard in the distance; they found it irritating because they thought they wouldn't hear the beginning of the next battle.

"The hush was solemn and churchlike, save for a distant battery that, evidently unable to remain quiet, sent a faint rolling thunder over the ground. It irritated, like the noises of unimpressed boys. The men imagined that it would prevent their perched ears from hearing the first words of the new battle."