Is there any way I can make a sound not as loud on an FX runner?

I imagine you'd either have to edit the effect itself or have the effect without sound and use a target_speaker in conjunction with it, or you could try

Key: volRange
Value: ### ### (e.g. volRange 100 300) - the numbers are min and max voume, so as you get closer to the speaker it gets louder.

Key: Radius
Value: ### (number is radius sound play within)
NB. this key/value will produce the wrong effect on a fx_runner - it should be used with the func_speaker.

Best bet for success - edit the fx file.

Can I just turn the sound off all together?

Maybe volrange 0 0 or radius 0?