Thanks d8veh
I have managed to sort the problem out, although it had nothing to do with the hub or cassette in the end! I have posted a few pics anyway as it might help the thread, but I never did manage to split the cassette down to grease the ratchet as I couldnt get it off. I did add some grease to a couple of the driveside bearings (by popping off the plastic side covers) as there wasnt a lot in there but I did nothing with the non drive side of the hub. When it was all back together there was no difference in noise whatsoever. By this time although frustrated I was able to recreate the squeak really easily and finally traced it down to......spoke nipples!
I noticed that there was some oxidisation on the rim around each nipple so out of curiosity I squirted some WD40 around every one and the noise went away immediately. No squeaks, graunching or anything. So there you have it, anyone with similar noises could give it a go, it might help. Not sure what the long term solution is though, a couple of rides in bad weather will dry out the oil and I dont really want to add another job to the regular servicing schedule. Thankfully I dont have rim brakes at least.
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