Back EMF is a killer, Seen it happen before but I would maybe check input voltage first.

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-Donald Hebig
-Stetsom, DD, Macrom, Powermaster, EFX
-Life Starts at 200 points

-Subwoofer design & modification expert
-Numerous Records, buisness awards, and vehicle cabin/enclosure design innovations.
-Team Audio Express 96-08
-Owner and engineer of the late Beyond Audio
-Professional car audio since 91' and never looked back