I take it then that you have seen the list of suggestions offered to cardinalfanrc and have tried those, making note of the results in each case. If not... take it one step a a time... don't change more than one thing at a time. Test, observe, record, repeat if necessary.
Experimenting with aim point and antenna elevation is usually one of the easiest first steps.
Loose connections, defective splitters, defective matching transformers, un-terminated splitter ports, un-needed or low quality amplifiers and damaged or defective coax are all (but not listed in any particular order) possible causes of single or multiple channel reception problems.
I notice in my neighborhood that many antennas are pointed 90 or 180 degrees off the line toward the transmitters. The axis of antenna boom should be parallel to the line from the transmitter and you location, and, the the shortest elements should be closest to the transmitter.
Proving and resolving interference
can be difficult but like any other trouble isolation step can be done methodically.
Finally, don't be too quick to say it can't be [....]. Also there can be more than one problem... (I met my wife while troubleshooting a Coast Guard Radar Control circuit that had a hardware failure and at least four separate maladjustment's. That gave a lot of time to get to know each other.
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