Hello Dane,
there is a bridging loop somewhere.
to break the loop disable one interface on Cisco switch side.
I would suggest to reconsider STP configuration on your side:
disabling STP is not usually a good choice.
You can try to make your switches less preferred for that vlan with a very high priority so that they are not elected root bridge
to avoid to feed with excessive broadcast from your side you can implement broadcast storm-control that works outbound
you may ask to the sonet provider if they can implement a similar function
Hope to help
Giuseppe