Those little beings can be found patrolling in groups of three in Cliff of Moher, near Myntaugh and his siabra distorters' camp. They love to catch you off guard after a tough fight against the siabras.
Lone ghoulies can be found at the frontier, in Cruachan Gorge and Mount Collory. Still annoying as hell, as they wander and attack on sight, but revenge is sweet as I slaughter them everytime I find some.