In reply to acharnley:
Did you contact Rab? If their customer service is any good (I don't buy Rab anymore), they should sort it out for you.
> It's had little use and very rarely with a small day pack.
Not to dismiss that, but the liner on my ME Morpheus (just plain Gore-Tex, not Pro) looks cleaner after half a decade of use? I wash it religiously, though. The discoloration might be due to a combination of sweat/dampness and a layer underneath?