They never got to the bottom of what was causing the problem. The symptom was that it squeaked loudly. The whole area was dismantled and replaced, the bearings were replaced, they even suggested at one point that it was the bottle cage bolts causing the problem. Nothing solved it however so eventually I got fed up and told them it either needed to be sorted once and for all or they needed to replace it. It went back to Trek's QC centre in the UK, was with them for two weeks, it came back allegedly cured and.... 5 miles down the road it was squeaking again.