Loud Snap at High Volume

I like to listen to orchestral music at fairly high volume.  I have Borresen Z2 speakers driven by a D'Agostino Progression Integrated in a fairly small room: 13x16x12.  At the peak of a crescendo, as you get in say the last movement of Mahler's 8th Symphony, the speakers will emit a loud snap, almost like the crack of a whip.  I haven't measured, but I doubt I have the level much over 90db.  I don't hear any distortion or break up before the snap. so it doesn't seem to be clipping.  Which I can't imagine happening with the power of the DAG (200w into 8ohms/400w into 4 ohm) into a relatively benign 89db sensitive speaker that doesn't dip much below 4 ohms.  I have read it could be loose speaker wire connections, and in fact the Shunyata Alpha V2 cable's banana connectors are not super tight at the back of the speakers.  Or could it be the Z2's ribbon tweeter breaking up?  Any insights would be welcome.