One's a problem, one's a question...

First, I want to change the spark sound for my levels. I've tried placing the new sparks.wav into both my mods ambience folder, and the half-life pak0.pak/ambience folder. Niether changed it and its still the normal one... So how do I change it?

Second, monsters. I've got a rather large hollow cylinder. Radius maybe 650 units (So a diameter of ~1300 units). There is a catwalk going around said cylinder's walls ~650 units above the bottom of the cylinder and an equal amount from the top.

Now I first wanted to put a tentacle in the bottom of the cylinder and have him try to attack you on the catwalk if you make noise. He however prefered to peck away at the walls or catwalk 180 degrees opposite me when I ran around. I tried putting info_node's to no effect.
Anybody know how to get the stupid thing to work right?