i changed the cambelt on my 1.8 zetec earlier, all seemed to be ok until i started it and it now sounds like a diesel and whines loudly. what have i done wrong?

i marked the cams and crankshaft before, and they still all line up perfect.

the car also drives perfect and revs up fine, sounds terriable though, the belt isnt too tight and has got fair amount of slack in it.

http://www.youtube.com/watch?v=s3hkTEQT8Io