Pretty much any 'ground hugger' type mob seems to aggro sound, and 'walker' types are sight. Granted there are exceptions, but stuff like toads, shrooms are usually sound and humanoid, beastmen, ogres are typically sight. Other than that, i've yet to see any indicators outside of the red triangle that would give us clues as to aggro type, sorry.
Edited, Aug 29th 2013 6:15pm by Dallie
Jerri Blank (Strangers with Candy):
"I may still be doing all the wrong things, but now i'm doing them the right way!"