My 28 yr. old house has a noise that is not related to squeeks or creaks or settling or hot/cold expansion cracks. It’s more like a continuous soft, dull, hiss or the noise you would hear with a seashell to your ear. It’s not coming from my HVAC duct work, and doesn’t seem to be coming from my plumbing. It doesn’t sound like its coming from the walls with my ear held to the wall. I’ve checked the electric door bell in the attic and other electrical appliances and that’s not it. I’ve checked for wood borers and don’t appear to have any. I thought it may be something off site like a new industry but don’t hear it on the outside of house. It’s not a street light buzz. The sound has only started within the last year. Any suggestions on what it might be will be greatly appreciated. Thanks, Going Crazy Dean