An often overlooked, but easy to resolve RF impairment are loose and/or dirty fiber optic connectors.  This issue often manifests itself as an increased noise floor when viewed on a spectrum analyzer.  The key to determining the difference between regular ingress and fiber connector noise is that the noise created by a loose or dirty fiber connector does not stop at the diplex filter roll-off frequency (typically 42 MHz in North America and 65 MHz Europe).  The image below shows a perfect example of this type of impairment: