Congested Network

Need some help figuring out where and if I have a bottle neck.

First of all I just started here and the network is in shambles. While in the server room I noticed the core Dlink websmart switch with vlan for dmz was flashing away like 2 blinks per second, all ports flashing at the same time except dmz vlan ports. This is why I started investigating this issue, well that and slow dmz backups.

I am new at sniffing traffic but started using Wireshark and mirrored my port to the trusted interface on the firewall and this is what I got from a 3 minute capture.

Protocol hiearchy
-TCP was 74% of traffic (data 19% and DCE RPC 21%)
-Arp was 22%

Total packets captured in 3 mins = 28107

I think something is wrong here?