Seatbelt warning possilby
Was it cold outside when you heard it? In many BMW models, there is a warning when the temperature is below 37 degrees Fahrenheit, because roads may be slick or icy. Many European cars have that.
Also, the clock has a memo button that, when set, will beep 1 minute before the hour.
^That is also true, I totally forgot about that feature. My X5 had that, it is part of the newer BMW radios under the "memo" section.
My money on temp
Looking for a Used 3 Series in your area?
CarGurus has 1,679 nationwide 3 Series listings starting at $1,499.
Search BMW 3 Series Questions
BMW 3 Series Experts