Lex is correct. I had to do the same thing with one of my fobs and decided to do them both.
Check your iDrive. In Settings, scroll down to 'Speed' where you can set a 'speed warning limit' which reminds you that you have exceeded it which is easy to do on the highway. The previous owner likely set it and that is what you are seeing and hearing. Find the setting and uncheck the box and it should not re-occur or set it to a speed at which you want a warning. Good luck.