My mother has had a smell in her house for past couple months. Apparently she only smells it at night and lately has smelled it from hot water tap. Had ducts cleaned, furnace people out to check furnace (fine) and others but no one can smell since they are there during the day... I haven't been there at night either so I haven't smelled it nor can I describe it although she says it's sort of a "chemical' smell (not rotten eggs). Since it's been longer than a few months, I'm sure it's not a dead animal in the attic. Any suggestions on what the problem is? She is getting very upset over this (82 years old)... thx.