IF done correctly, it might make the thing very scary. But that's very hard. Music always helps a lot for supsense.
You don't even need fancy sound scores. There are lots of cd's which offer their own sounds (fx/music etc) for free. Like magix soundpool. Or you could go with strings all the time of course. Or a faint background echoing noise. But if you really want to let the audience to know there's something scary happening, pick up a mic and sing your own score. "Ooh its scary. Something scary is happening here. Very scary. This is a very scary, momeeeeent". I did that for my last flick and it helped immensely.