On a 2012 ACE we had, it was considered a defect and was corrected under warranty (not sure how that applies to your used coach). Basically (going on memory) The track and it's alloted space was too small and actually hitting. It had to be removed, cut and reinstalled. it's been fine since. I think the harsher noise that you are experiencing was a defect vs the rubbing noise a lot of coaches experience are different. My slide seals on our 2013 29.2 still sqeuak a bit. I have lubed it a lot, moving to talc powder next.
On the used ACE you may want to conatct the dealer (if you bought from one) or contact Thor to see if they will warranty it.