SIM 7.2 handles traps differently that previous version of SIM. If you install the hotfixes for SIM 7.2 it will help the issues by cleaning up the traps folders periodically.
I have seen this many times and this will eventually bring SIM to a crawl unless you install the hot fixes. The worst site I've seen had 1.8 million traps. What I have seen cause this is where you have the authentication button checked on your management systems. This button is under the security tab under the SNMP service.
Send authentication trap: Specifies whether to send an SNMP trap message to all trap destinations if this SNMP host receives an SNMP request from an SNMP host or community that is not listed on the Security tab. Authentication is the process of verifying that a host name or address is valid. When the SNMP agent receives a request that does not contain a known community name or that is not sent from a member of the acceptable hosts list, the SNMP agent sends an authentication trap message to one or more trap destinations, indicating the failure of authentication. This check box is selected by default.
You could run SNMPutil on one of your managed systems to see who is trying to do a SNMPget against it. In several cases I have seen Solar Winds ro be the culprit but it could be any tool using SNMP that would cause this.
An easy fix would be to push out a GP with the authentication flag disabled