Hi,
Any SNMP management tools, will have a periodic polling cycle to gather the statistics on the switch. For traffic related statistics, snmp uses a counter value to record the utilisation. The snmp tool will calculate the traffic statistics as follows.
X = Value gathered from the switch, during the previous polling.
Y = Value gathered from the switch for current polling
Z = Polling interval in Seconds.
Traffic Rate/second => (Y - X) / Z.
As you can see from the above formula, the snmp tool will provide only the average rate of the traffic statistics.
This might not give you an idea about the sudden traffic bursts from the snmp tool.
Occasional spikes are OK, if they are really due to any legitimate traffic from the attached devices on those switch ports.
If they are recurring frequently, you might have to examine what kind of traffic is flowing and investigate the details of devices connected on those switch ports.
Establishing a SPAN session for those ports and capturing the traffic using a ethernet packet capture tool ( like sniffer/ ethereal) will assist you to investigate those sudden traffic bursts and nodes which are creating such traffic.
Hope this helps
-VJ