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Question: Flickering every 10-15 seconds or so after hooking cable box up

I have hooked my cable box up to the sound system and then the sound system up to the tv...it's all sony, the cable box runs fine off the tv alone but when I hook it up to the sound system (all with HDMI cables)it flickers every 10-15 seconds for a couple seconds then is fine again but repeats which is annoying...just wondering if anyone else has had this problem or may know what may be causing it?