I have the same problem with all of my Axiom speakers except the EP600. The grills work themselves loose in 2-3 days. I have to snap them back into place manually.

4 M80s/VP150/EP600/Denon AVR-5308 & DVD-2910/
2 QSC SRA3622(1100wattsX2)/Carvin 1800HD(600wattsX2)