1. On the 'Create Sample' screen - on input (in between Thresh and Dither) - what is that set to?
2. Have you checked the cable - try plugging the left cable into the right and see if there's any difference.
try switching the cords around. I mean, take the left on the sampler and swap it with the right. That way you know if its the cord, or maybe the imput. But I think its just something youve overlooked somewhere