Gnolls are similar to the were-hyenas of African bushman folklore, and the tall dog men (Cynocephales) of early European travellers' logs and bestiaries. Hyenas were associated with death because they dug up and ate human corpses.
Gnolls in the Discworld series are small, matted and dirty enough to sprout fungi and grasses on their hides (and seem to relate to soil as trolls relate to rock), and act as street-cleaners in cities like Ankh-Morpork; as Captain Carrot Ironfoundersson puts it, they "pick up this, pick up that, maybe bang it against the wall until it stops struggling..." In the case of at least Stoolie, if not every gnoll on the Discworld, there seems to be a tendency to drop the vowels in words, reflecting a croaking sort of voice.
Dungeon & Dragons Version
World of Warcraft version: