This is usually a simple fix. Noise in a contact center can be eliminated by good quality headsets. Here is an example of your noise problem:
If you have 10 agents sitting side by side with monaural headsets (headsets with one ear piece) when the first agent speaks to a customer, the second agent has to speak louder to overcome the noise of the agent beside them, likewise this continues over all agents like a domino effect. Each agent speaks louder to overcome the noise of other agents speaking.
However if you look at binaural headsets where both ears hear the customer then agent do not need to speak as loud as they do not hear the other agent beside them speaking.
Take a look at these: http://www.vxicorp.com/products/contact-center-and-office-solutions/corded/passport/
This should certainly help your problem but may not eliminate it as there are other factors like space between agents and call centre environment that may contribute to overall noise.