Problem
We have seen quite a few issues where we see double the expected utilization/rate on an interface or interfaces.
While there may be some Netflow configuration issues that need to be corrected, one of the first things to check for if the interface has WAAS with WCCP enabled.
If so, there is a known issue with Cisco where WAAS with WCCP enabled causes double the NeTflow data to be sent resulting in double data seen in reports for these interfaces.
Solution
This is resolved in newer releases of Cisco's IOS's, you should check with Cisco support for the proper procedure of correcting this for your specific device.
I do not currently have the list of affected Cisco IOS's but Cisco support should be able to provide this.