No, swapped out both front and rear with new resin Shimano pads about a month or two ago. So not new new, but not worn I would say; plenty of material left on both sets. BTW, for some reason Bikeforums is only letting me type 5 messages every 24 hours, so apologies if I don't reply for another day or so haha. All the advice is seriously appreciated, thanks all! The fact this has stumped me (which is unsurprising), as well as 2 LBSs, leads me to believe this is a pretty uncommon/hidden issue (at least something that wouldn't appear to the naked eye, such as a bent axle).