An old saying that we may not even understand the meaning of but use more often than we are aware. When you knock on someone's door, it's sometimes that bop bop ba-bop bop (pause) bop bop rhythm.
It has the air of comfort or safety, that the person using it is someone that you know, unthreatening and wanting your attention, your company. Not likely to be used by the ATF thugs upon breaking into your abode to seize your homegrown crop of pot plants you have in the basement, unless they catch on. Shh…it's our secret.
When I hear a car honk in that series of beeps, and I always regard it as a pleasant sound, since it's used to draw someone out of their house and into the world.