" Eragon and the others walked as quietly as they could, but the tunnel magnified sounds. Every bump and scrape echoed, filling the air with a multitude of overlapping whispers that seemed to murmur and sigh with a life of their own. The whispers made Eragon feel as if they were surrounded by a host of disembodied spirits who were commenting on their every move.
So much for sneaking up on anyone, he thought as he scuffed his boot against a rock, which bounced against the side of the tunnel with a loud clack that multiplied a hundredfold as it spread through the tunnel.
“Sorry,” he mouthed as everyone looked at him.
A wry smile touched his lips. At least we know what causes the strange sounds underneath Dras-Leona. "

― Christopher Paolini , Inheritance (The Inheritance Cycle, #4)