If you are seeing, one or more interfaces in a port-channel is getting utilized more than than others, you may need to look in to ether channel -Load balancing algorithms.
In case of catalyst switches, "source mac" will be the default one used for load balancing.
You can refer below cisco article and change Load balance method based on your needs
http://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/12023-4.html
Also you can verify the same using below command
#show etherchannel load-balance
But if you want to change, it will be a global command and will affect all channels
config#port-channel load-balance <new method>
