When multicast MoH is enabled on a Cisco IOS gateway, multicast source entries that have the address of the router interface are registered, and Real-time Transport Control Protocol (RTCP) packets are sent from the gateway. If the network is large, this can cause a multicast storm.
Further troubleshooting shows that the Cisco Catalyst Communications Media Module (CMM) virtual interface for the ACT module makes an assumption and incorrectly advertises as the multicast Rendezvous Point (RP) interface.
This symptom is noted as a defect in which a router interface can incorrectly advertise multicast traffic, when triggered by multicast MoH. The defect is documented in Cisco bug ID CSCeb87233.
In order to resolve this issue, tune the ip rtcp report interval command to decrease RTCP multicast traffic. This problem is resolved in Cisco IOS version 12.4(8a).