Hi
Whats the firewall you have ?
if you can afford some downtime, then you will be having a choice to figure out whats happening by narrowing down the issue if its related to the environment
try after each of following points to monitor the CPU utilization:
- disconnect uplinks to other switches
- disconnect redundant links if you have.
- disconnect Firewall link.
- if you have left up with only end devices ports then it could be from one of these ports.
try also to syslog only Critical info.
Good Luck !!!