I had a loud hi frequency squeal coming from the front grill of my 2009 FX35 with the ignition off which persisted for more than 36 hours. The sound was unbearable and was heard up and down the street as far as a city block away. The only other symptom I had was the dash display which shows the outside temperature showed only ICY and three dashes where the temp is supposed to appear (---) and F (for farenheit). The sound came directly where I believed the sensor is located (right front lower grill area). I didn't need to use the car and the sound was muted when inside my house so I planned to take it in to the dealer Monday morning, but the next day it just stopped, and I haven't had the problem again. Now that I know the location of the sensor, if it happens again, I will pull it out and replace it. However, in the case of the missing sensor, it may be that is why it was missing. As far as I can find, there is no TSB or recall on the part, and I can find no one else who had the problem.