I don't know where you live, but since it is getting colder these nights, your "problem" might be a programmed feature. When the outsside temp gets to 37 degrees or colder, the computer automatically switches the OBC to the temp readout, and then makes a chiming noise to alert you. This tells you it is cold enough for black ice to form on the roads. It is a safety feature, and mine came on this AM, as we had an unusally cold morning here in San Diego - 35 degrees.
Hopefully this is all it is.