Scott, we are having the same popping and rack wear issue right now with our ACE 29.2.
Ours is a 2016 model with about 30,000 miles. No idea on how many cycles on the slide going in and out, but I would say a lot. We tend to keep moving, never in one place for more than 3 or4 days. Our top rack, drivers side, got so worn, it took 2 people to push the slide out enough for the gear to engage. After that, the slide worked normally. On retract, the slide would never make it in that last 1/2 inch.
I urge all owners to check for rack wear regularly. Bus is at Camping World now for repairs. Hopefully the extended service plan will cover it. I doubt it though.