Final solution: new woofer arrived this evening, and the M60 is now great! No ratling metallic sound (except when the room shakes! ).

Thanks everyone for their suggestions, and thanks Axiom for their great customer service!

P.S. - So great, in fact, that they let me keep the 5.25" driver they sent by accident as a spare, since they asserted it was their fault for sending me the wrong driver!



---- A Woofer in Tweeter's Clothing... M60s, VP150, QS8s, EP350 Onkyo TX-SR702, Denon DVD-3910