One reason may be that you are sniffing a switch and that you are not really seeing all the traffic. Make sure you mirror the backbone to your port to see as much of the data as possible. Otherwise you will have lower traffic flow and all the broadcast traffic will seem high.
I sometimes take a look at broadcast traffic without a mirrored port and it is always 20 times higher percentage wise because of the lack of data flow.
In working on my current network position I did find that they had been creating network printers with a direct connect to the ip address and then changing the ips and readding the printers again thus leaving the old ports configured in the pcs. And of course the pcs arp broadcast like crazy looking for the printer port even though it is not in use.
Oh I know this is a very old thread but I wanted to leave this out here for anyone researching arp issues.
