A very dusty environment can cause dirt to build up in a Cisco router in turn causing a Serial Interface Card to malfunction and spew out more CRC errors than data which in turn causes very high round trip times and packet loss.
We only found this after several days of troubleshooting and fixing other problems at this C-band VSAT site. Problem solved by opening up router and using a vacuum cleaner. No engineering involved; just plain old cleaning. Of course this would not have been necessary in a clean environment.