I had something similar about 2 years ago. Went for a drive in the country with the Mrs and the boy one Saturday. It started raining really heavily. I had to stop for something and then when I started off again there was the most almighty and horrible screeching noise. It was constant, the moment the car moved it was there and I thought it was something really bad. I very gingerly limped the car home and parked her up ready to limp her to the garage first thing Monday morning. It had been coming from the front passenger side. I jacked it up that evening, spun the wheel and had a look around with the torch. All seemed fine. I was convinced it was something serious to do with the break mechanism or CV joint, or bearing or something internal, out of sight.
Anyway, Monday morning, pulled away expecting the noise again, only there was nothing. I drove for a little while expecting it to come back, but still nothing. Popped over to Honda the next day who gave the car the once over and they could find no sign of any damage to the wheels or anything that would have caused the noise. Although the had informed me that my front roll bar had snapped at one end, although apparently they said it was unlikely that this would have been anything to do with noise I was hearing. They said the most likely culprit was a piece of grit finding its way between the disk and pad.
Either way, the noise has never been heard since and it meant I also got another problem caught early before it did any further damage to the car.
