I Occasionally Experience A Strange Smell. It Is Consistently The

I occasionally experience a strange smell. It is consistently the same smell. My wife doesn't seem to smell anything out of the ordinary. I have "sniffed" around the house, in the basement, in the garage, even in the crawl space for its source. Nothing turns up. It is not a bad smell. Not particularly musty. It is a smell similar to the smell that appears from charging my camera batteries. A little like vinegar. I don't seem to have any other symptoms. Stomach is stable. No headaches. I am 76 years old male in good cardio-vascular condition.