At first, he thought it was windchimes. Just before the first hallucination, after he'd compartmentalized the hellfire burning in his brain as best he could, the metallic clinking made Sam think Bobby had put up wind chimes as an extra measure of protection for the house. He forgot to look for them or ask about it when he saw the meathooks all over the basement.
A few weeks passed. Bobby buried deeper and deeper in his research but still came up empty. Dean threw himself into fixing the Impala to put off dealing with what Cas had become and what he wasn't sure was happening to Sam. Sam helped where he could, and kept hearing that damn clinking before every hallucination. By now he knew they weren't chimes, they were whatever was rattling in his head.
It wasn't until Lucifer finally showed himself that Sam realized what he'd been hearing. It was the rattling of chains. More specifically, it was the rattling of Sam's chains.
AN: IDK, they sounded like chimes to me but it bothered me because it didn't make a whole lot of sense so this happened.