I'm getting some strange looking graphs on some ports on my routers, where the graph is basically just a bunch of spikes. Set at 1 second intervals, it will register traffic for one tick, then nothing for anywhere from 4-10 ticks, then register traffic again, and so on. This is happening on Cisco 2811's, 2911's, and a 7206VXR, and it happens on the FastEthernet, GigEthernet, and SVI ports on them.  If I set the interval to 5 seconds or higher, it looks normal again. Now, these same routers with this problem have no issue doing a 1 second interval on their Serial ports or sub-interfaces. We have several 2960 switches that seem to work just fine.