I tuned to 1690 khz with my Sony ICF SW7600GR. My target was a station in Colorado. After a couple commercials at the top of the hour, a new age-style song came on. And it kept coming for the next 15 minutes! It's a simple melody with a pan-flute type instrument, backed by a piano.
I looked up the possible stations for 1690 khz in the USA, and found these at the FCC site:
KDDZ: Arvada, Colorado
KFSG: Roseville, California
WMLB: Avondale Estates, Georgia
WPTX: Lexington park, Maryland
WVON: Berwyn, Illinois
I can't find a website for KFSG. If I could, I'd see if it had a live audio stream so I could compare it with the broadcast. But it's supposed to be a spanish station and the ads I heard were in english. KDDZ is Radio Disney, so that doesn't seem to be a candidate either.
Stations in Toronto, Montreal, and the Virgin Islands also use this frequency. Maybe this is a new station that has commercials ready but no actual content, or they're testing a transmitter. I'll keep monitoring this signal to see if I can solve the mystery.