My 2015 Legacy Limited with Nav, Eyesight, and Keyless Entry suddenly started a random one-note interior "Beep" (sounds more like "Boink") from the driver's door speaker, primarily when on a narrow road with woods and a slight embankment on either side, but very occasionally on a wide open flat road with nothing but empty farm fields to either side. When stereo is on, the volume drops, it "Boinks" once, then volume returns. Only reference in the main owner's manual to a single beep warning indicated a possible low battery in the keyless fob. Put a new fresh battery in, no luck, still does it. Tried the other fob. No luck, still does it. Nothing in the other manuals -- Eyesight, Nav and Multimedia, etc., about an audible beep. Also tried it with and without cell phone turned on -- no effect, still "Boinks" whether phone is on or off. It seems to be related to geographical location -- in other words, it "Boinks" on the same roads, and the same general location on the road. No warning lights illuminate when it beeps, either on the instrument panel of on the Nav/stereo screen -- it's strictly just the audible beep. I have tried the settings menu on Nav/stereo screen, but nothing is shown. Anybody have any ideas? It's driving me crazy.