I have an EB and when I give her a squirt on the noisey pedal, then back off its seems to whine (gearbox, it sounds like the jetsons car) and carry on, then the diff seems to make a clunk noise, and this is only while its in 'POWER' mode, in economy mode it runs fantastic, I used to drive really crazy but now I have backed off (I find this a lot cheaper..) and I have noticed this noise only now.

If it only happens in Power mode its got to be a Transmission problem.
Take it to a Transmission Specialist and get them to take it for a drive.