In my unfinished basement there is a hissing sound. Not sure how long it's been going on but do know that it's not constant. I have a radon mitigation system and always attributed the noise to that system. Today the sound seemed to be coming from a slightly different area (same wall, but further away from the radon system). We investigated and found that the hissing seems to be coming from a crack where the basement floor meets the wall. Should we be concerned? I'm thinking that we should fill this crack but not sure what to use to fill it. There's no gas in the neighborhood so no worries from that aspect. We don't typically have water in the basement but do run a dehumidifier in the warmer weather. We did have water in the basement on 2 separate "100 yr" storms but were able to keep water to ankle depth by lots and lots of wet vac'cing . Recommendations on what to use to fill the crack?