I had the same problem with my second 451. It turned out to be the clockscrew under the airbag. It only happened whence inside temperature was 120+ degrees.I have a 2013 Gas Smart Car with about 40,000 miles.
On Wednesday I washed my car. On Thursday it rained. On Thursday afternoon I was driving home from work and I made a sharp left turn into a drive thru, and I thought a car beeped at me.
I heard a very faint horn like sound. I soon realized, it was my Smart Car making this sound. It makes this sound every time I make a left turn, and it comes from the front of the car. The best way to describe its is a muffled horn sound. Sometimes, it makes this sound when I'm stopping and going, or taking off from a green light. But its always happens when I make a left turn.
I read somewhere that it's my brake pads telling me its time to get them replaced.
I wanted to know if anyone has had this problem, and if it is in fact the brake pads?