We are on well system w/ water softener. In upstairs 2 bathrooms cold water from faucets has strong "swampy" smell (probably sulfur, but I'm not sure what sulfur smells like) if faucet wasn't used for couple of hours. Smell goes away after about a minute. Didn't notice smell in downstairs faucets, which leads me to believe it's in pipes? Is there any way to get rid of it? Smell wasn't as bad when we moved it (early spring), but seems to be getting stronger (maybe because of rising temperatures). We also have tankless water heater (part of oil boiler), but smell is mostly in cold water.