The over extension theory got me curious and I compared the travel of the drivers in each speaker. Oddly enough it appears the one that is popping is moving less (not just one but all drivers in that speaker). I guess this is just another reason to take it in to see the Axiom Doc

LFR 1100s QS8s QS2s ADA15000-4, VP 150, M 3s,Polk CSI A6, Klipsh B10B, SVSPB2000,PSW125x2