Clanking Leather Armor (3.5e Equipment)
From D&D Wiki
Clanking Leather Armor: This well worn and softened piece of masterwork leather armor has a strange enchantment cast upon it.
When being used normally, it provide a -1 to armor checks, as with all masterwork armor, and is mostly silent.
However, whenever it is worn while the character attempts to sneak, it clanks, like a suit of full plate armor.
In game terms this equates to a -10 on move silently rolls, and a +5 to any listen checks performed to locate the sneaking creature.
 GM Notes
The origins of the Clanking Leather armor actually centered around a specific druid, named Mandel. He was a proficent druid, and became very powerful during the course of his many adventures. His famous leather armor was actually a fairly common piece of +2 leather armor. What made it clank though, was his dice rolls.
Mandel never rolled above a 5 for his sneak tests, and it became a running joke that he could make leather 'Clank'.
His skills seemed to have passed onto our current druid, who can't sneak worth beans.