It would help us greatly if you could use these analysis tools to create a report that reflects your actual antenna location (including elevation). When you have those, please post them. Please include the FM report as an aid to diagnosing possible interference.
http://www.tvfool.com/?option=com_wrapper&Itemid=90
http://www.fmfool.com/?option=com_wrapper&Itemid=29
Finally, can you describe what type antenna(s) are installed and where they are (set-top, attic, tower...), any amplifiers, combiners, splitters, etc.