300tdi gear box metalic knocking noise

Hi All Happy Christmas
I have a 300tdi disco. I thought the front diff needed changing I haven't git round to it yet. the other day when I accelerate I get a metallic knocking noise so I thought that's the diff finally giving up so I removed the front prop shaft in the snow, put the diff lock on and drove the car I am still getting the noise so I assume it must be gear box related any Ideas.

cheers

simon

Now do the same but removing the rear prop, replacing the front prop.

I'd guess it's just as likely, however, to be the handbrake or a UJ