Patient: "Doctor, doctor, it hurts when I do this."

Doctor: "Well don't do that."

Some truth to the (old) joke. If you SNMP poll, the router needs to use CPU cycles to respond. There's not much you can change on the router that will reduce SNMP CPU (except perhaps on traps/informs). However, there's much you might change on the external SNMP requestor. Items such as polling frequency, what's being polled, and sometimes even how it's being polled, can be most important.

A different but perhaps more important question is, is the high SNMP CPU utilization adverse to the router's primary functioning? Assuming there's ample CPU to service all processing, a 100% busy CPU, alone, might not be an issue.