Alter Aeon Online Help

Keywords are:  'humming noisy noise'

An item that has a 'hum' flag is an item that either makes noise or
is loud when used normally.  Examples would be clanking armor, a box
full of chickens, and Blasdell's Screaming Orb.

If you wear items that are humming, you will be unable to sneak or hide.
Humming can be removed from an item with the necromancer 'silence'
enchantment.