judering and clunking noise?

I need some help and advice

my car has been shaking for a while at 40 to 50 mph but today i was driving and it lost power slightly like the clutch slipped after that it started to judder and make a small permanent grinding noise and a big clunky noise. it feels like a half shaft has gone but they seem to be ok. it is definitely something to do with the drive but i can't pin down what it is? any help would be much appreciated.

Oli

it also feels like its at the front end, possibly the gear/transfer box.

whats with no replies, is it me or am i missing something here

check prop shaft UJ's

ok, I've checked the prop shaft ujs and they are not the problem, i took the front prop off and took it for a drive and there is a metal on metal grinding noise as well as the clucking, I've been under it but just can't work out what it may be. when i let off acceleration or put the clutch in it seems to die down considerably. does anyone have any ideas what it may be?

Have you jacked it up front end (if you are sure thats where the noise is from) turn each wheel and check wheel bearings and swivels for movement etc?