Just run a good signal (BR, DVD, etc) through the system at the same volume. If the anomaly appears from clean sources like these, you need to move down the chain and check the AVR, and the speakers. If not, it is just a cable issue. While on cable, you can also change the wiring so your center sound (in DD) is routed to one of your mains. If only the right speaker (for ex.) now has the sound (and you are using a clean source) you have a problem with the center channel of your amp. If the anomaly stays in the center channel even when the center is using the signal for the Right channel, you have a problem with the center speaker and should call Axiom.
I don't know your cable company, but cable loves to compress information as much as possible. The more compression they can get away with, the more channels they can shove into their allotted bandwidth. Locally, they shove well over 300 channels down the coax line, and I know other places have even more. My guess is that your cable company is just compressing the audio track so it sounds like a bad MP3 records, with harsh frequency response in the highly compressed zones. Here the sound is fine, but we get tiling and other visual anomalies from compressed cable.
Also, try watching in stereo so the center sound is spread to the main speakers. If it is the cable, you should get the same anomalies in the mains - unless the issue with DD decoding, at which point I'm not sure you could trust a test in stereo. Others will join and get you through this. Do you have access to satellite TV, perhaps that would be your best and most cost effective solution? Best of luck; with a system like that (assuming your amp is of equal quality) you should not have to deal with fatigue or make severe tone changes to enjoy it.
