Onkyo TX-NR818 & Dish Network 722k issue

Haven't been able to find any info, so thought I'd post my ? here, I bought a nib 818 early Feb, all went well etc then 5 days into ownership, noticed a pronounced thump from the sub while watching tv & the listening mode changed from programming to commercial etc. Played with all the audio settings on the 818 to no avail, then turned sub off & put the Polk A7s on Full Band & even then, still a thump from the 7s subs! Thought this must be a defective unit since I didn't have this issue with the avr the 818 replaced (Onkyo HT-RC180) so sent it back for a replacement. Got the new unit Tues, set it up, & I'll be danged if the thump is still there! So thought it must be the old hdmi cables I'm using, bought them 5 or 6 years ago, so got new ferrite core cables & that did improve pq & channel switching a lot. With the old cables there had been some delay for channels to switch but never put much thought into it until I started having thump issues. So it finally dawned on me to look into the 722k's audio setup & tried turning off Dolby Digital & just use PCM, RF & tried Line only & still a thump. Turned volume levelling off & no thump! Only downside to that is now SD channels are much louder than HD but that's what the volume button is for I guess. Just curious though if the Dish processes volume levelling could really affect the 818 in such a way? Thx!