Need to monitor internal network traffic

I'm trying to determine if a piece of equipment in our network is causing excessive traffic.

We have 2 48 ports switches
2 physical 2008 R2 servers.  1 is a Virtual Host, which has 3 virtual servers
From our server room there is a Fiber Optics connecting our main building to a second building.
In the building where the Fiber terminates there is a 16 port switch that connects to 8 physical network jacks.
There are 4 computers connected to individual network jacks.  
There is a 5 port switch plugged into one network jack.  Into the switch there are 2 printers and 1 computer.
On one of the servers is an Access Database.
In the morning when accessing the database and opening a form, the process time is 7 seconds
Mid afternoon opening the same form the time is 30-40 seconds

What I'm hoping is available is a application that can constantly monitor the speed from the building that has the 7 computers and check the speed back to the main building.

With this application monitoring the speed, I'll be able to tell when the speed drops off.  Then I can begin the process of determining if a piece of hardware is causing the problem.  I can unplug one computer at a time.

NOTE:  We just replaced the Fiber Optic boxes in both buildings and the 16 port switch.  The speed was fast after we did this.

If there is a better solution PLEASE tell me. Keep in mind we are Non-Profit (Society for the Prevention to animals) so I don't have a lot of money to spend.