Driving down the road just now I started hearing a loud metallic 'squealing' noise & thought bloody hell - thinking it was someone else's car. Then I didn't drive away from the noise so I wound my window down to hear the noise was my car. 
I checked the handbrake was off properly. The car still moved forwards ok & the breaks were ok. No smell of burning. As I was only one street from home I crept back (noise still going) & parked outside. As I manouvered the car to the kerb there was a sound like a piece of metal falling to the ground. I got out & peered underneath but there's nothing there. All 4 tyres are ok. What the fuck has happened? I'm scared to drive it anywhere now - even to the garage to take a look at it. Any ideas?